WO2016132613A1 - Oblique-view objective optical system and oblique-view endoscope equipped with same - Google Patents

Oblique-view objective optical system and oblique-view endoscope equipped with same Download PDF

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Publication number
WO2016132613A1
WO2016132613A1 PCT/JP2015/082288 JP2015082288W WO2016132613A1 WO 2016132613 A1 WO2016132613 A1 WO 2016132613A1 JP 2015082288 W JP2015082288 W JP 2015082288W WO 2016132613 A1 WO2016132613 A1 WO 2016132613A1
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Prior art keywords
lens
optical system
objective optical
lens group
conversion element
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PCT/JP2015/082288
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French (fr)
Japanese (ja)
Inventor
高杉芳治
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オリンパス株式会社
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Application filed by オリンパス株式会社 filed Critical オリンパス株式会社
Priority to EP15882714.7A priority Critical patent/EP3260899A4/en
Priority to JP2016539333A priority patent/JP6001227B1/en
Priority to CN201580027281.2A priority patent/CN106461920B/en
Publication of WO2016132613A1 publication Critical patent/WO2016132613A1/en
Priority to US15/342,352 priority patent/US9775494B2/en

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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B1/00—Instruments for performing medical examinations of the interior of cavities or tubes of the body by visual or photographical inspection, e.g. endoscopes; Illuminating arrangements therefor
    • A61B1/00163—Optical arrangements
    • A61B1/00174—Optical arrangements characterised by the viewing angles
    • A61B1/00179—Optical arrangements characterised by the viewing angles for off-axis viewing
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B1/00—Instruments for performing medical examinations of the interior of cavities or tubes of the body by visual or photographical inspection, e.g. endoscopes; Illuminating arrangements therefor
    • A61B1/00064—Constructional details of the endoscope body
    • A61B1/00071—Insertion part of the endoscope body
    • A61B1/0008—Insertion part of the endoscope body characterised by distal tip features
    • A61B1/00096—Optical elements
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B1/00—Instruments for performing medical examinations of the interior of cavities or tubes of the body by visual or photographical inspection, e.g. endoscopes; Illuminating arrangements therefor
    • A61B1/00163—Optical arrangements
    • A61B1/00174—Optical arrangements characterised by the viewing angles
    • A61B1/00177—Optical arrangements characterised by the viewing angles for 90 degrees side-viewing
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B1/00—Instruments for performing medical examinations of the interior of cavities or tubes of the body by visual or photographical inspection, e.g. endoscopes; Illuminating arrangements therefor
    • A61B1/00163—Optical arrangements
    • A61B1/00186—Optical arrangements with imaging filters
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B13/00—Optical objectives specially designed for the purposes specified below
    • G02B13/04—Reversed telephoto objectives
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B23/00—Telescopes, e.g. binoculars; Periscopes; Instruments for viewing the inside of hollow bodies; Viewfinders; Optical aiming or sighting devices
    • G02B23/02—Telescopes, e.g. binoculars; Periscopes; Instruments for viewing the inside of hollow bodies; Viewfinders; Optical aiming or sighting devices involving prisms or mirrors
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B23/00—Telescopes, e.g. binoculars; Periscopes; Instruments for viewing the inside of hollow bodies; Viewfinders; Optical aiming or sighting devices
    • G02B23/24—Instruments or systems for viewing the inside of hollow bodies, e.g. fibrescopes
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B23/00—Telescopes, e.g. binoculars; Periscopes; Instruments for viewing the inside of hollow bodies; Viewfinders; Optical aiming or sighting devices
    • G02B23/24—Instruments or systems for viewing the inside of hollow bodies, e.g. fibrescopes
    • G02B23/2407—Optical details
    • G02B23/2423—Optical details of the distal end
    • G02B23/243—Objectives for endoscopes
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B23/00—Telescopes, e.g. binoculars; Periscopes; Instruments for viewing the inside of hollow bodies; Viewfinders; Optical aiming or sighting devices
    • G02B23/24—Instruments or systems for viewing the inside of hollow bodies, e.g. fibrescopes
    • G02B23/26—Instruments or systems for viewing the inside of hollow bodies, e.g. fibrescopes using light guides
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B1/00—Instruments for performing medical examinations of the interior of cavities or tubes of the body by visual or photographical inspection, e.g. endoscopes; Illuminating arrangements therefor
    • A61B1/04—Instruments for performing medical examinations of the interior of cavities or tubes of the body by visual or photographical inspection, e.g. endoscopes; Illuminating arrangements therefor combined with photographic or television appliances
    • A61B1/05—Instruments for performing medical examinations of the interior of cavities or tubes of the body by visual or photographical inspection, e.g. endoscopes; Illuminating arrangements therefor combined with photographic or television appliances characterised by the image sensor, e.g. camera, being in the distal end portion

Definitions

  • the present invention relates to a perspective objective optical system including an optical path conversion element and a perspective endoscope including the same.
  • image sensors such as CCD (Charge Coupled Devices) and C-MOS (Complementary Metal Oxide Semiconductor)
  • pixel miniaturization and element miniaturization are progressing due to progress in miniaturization technology.
  • an image sensor having very fine pixels for example, an image sensor having a pixel pitch of about 2 to 3 ⁇ m has been manufactured.
  • recent image pickup devices have become smaller and have a larger number of pixels than before.
  • the lens outer diameter and the overall length of the optical system are reduced, it becomes difficult to make the light emitted from the optical system incident perpendicularly to the light receiving surface of the image sensor.
  • the light ray is incident obliquely on the light receiving surface (hereinafter referred to as “oblique incidence”).
  • recent imaging devices such as CCDs and C-MOSs are designed on the assumption that the optimum light beam incident on the light receiving surface is oblique incidence.
  • recent image sensors have oblique incidence characteristics.
  • a high-performance optical system is, for example, an optical system with high resolution and good aberration correction.
  • perspective objective optical system as one of the objective optical systems for endoscopes.
  • forward view, side view, or backward view is performed.
  • FIG. 1 is an example of a conventional perspective objective optical system.
  • the perspective objective optical system 1 is a perspective objective optical system that performs a side view.
  • the oblique objective optical system 1 includes a front lens group 2, a prism 3 and a rear lens group 4.
  • the optical axis of the front lens group 2 and the optical axis of the rear lens group 4 are orthogonal to each other by the prism 3.
  • FIG. 2 is another example of a conventional perspective objective optical system.
  • the perspective objective optical system 5 is a perspective objective optical system that performs forward viewing.
  • the oblique objective optical system 5 includes a front lens group 6, a prism 7 and a rear lens group 8.
  • the prism 7 causes the optical axis of the front lens group 6 and the optical axis of the rear lens group 8 to intersect (but not in an orthogonal state).
  • an optical path conversion element having a large glass path length is arranged in the optical system. For this reason, particularly in a perspective objective optical system, a large space for arranging an optical path conversion element such as a prism is required. As a result, in the perspective objective optical system, the total length of the optical system is longer than that of the direct-view objective optical system. Thus, since the perspective objective optical system tends to be larger than the direct-view objective optical system, the perspective objective optical system is required to be further downsized.
  • Patent Documents 1 to 5 disclose perspective objective optical systems.
  • the perspective objective optical system disclosed in Patent Document 1 includes a front group diverging lens system and a rear group converging lens system.
  • This perspective objective optical system is an optical system premised on being used for an image fiber. For this reason, in this oblique objective optical system, the light beam emitted from the oblique objective optical system can be incident substantially perpendicular to the incident end face of the fiber.
  • the perspective objective optical system disclosed in Patent Document 2 includes a first lens group including one negative lens and a second lens group having a positive refractive power.
  • a glass material having a small dispersion (a glass material having a large Abbe number) is used for the negative lens and the prism of the first lens group in order to correct chromatic aberration.
  • the perspective objective optical system disclosed in Patent Document 3 is composed of a front group having a negative focal length and a rear group having a positive focal length.
  • the perspective objective optical system disclosed in Patent Document 4 includes a first lens group composed of a single lens having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power. And is composed of.
  • the third lens group is composed of a cemented lens composed of a negative lens and a positive lens in order from the object side. In this way, telecentricity is ensured. That is, in the perspective objective optical system disclosed in Patent Document 4, a light beam emitted from the perspective objective optical system can be incident substantially perpendicularly to the light receiving surface of the CCD.
  • the perspective objective optical system disclosed in Patent Document 5 includes a negative first group and a positive second group.
  • the optical system is held by a frame member.
  • the optical system is attached to a jig for assembly through a frame member at the time of assembly. Further, the assembled optical system is assembled into the endoscope distal end portion via the frame member. Therefore, it is necessary to secure a certain length for the fitting portion of the frame member.
  • FIG. 3 is an example of a frame member of the perspective objective optical system.
  • the perspective objective optical system 9 is a perspective objective optical system that performs a side view.
  • the oblique objective optical system 9 includes a front lens group 10, a prism 11, and a rear lens group 12.
  • the optical axis of the front lens group 10 and the optical axis of the rear lens group 12 are orthogonal to each other by one reflection at the prism 11.
  • the front lens group 10 and the prism 11 are held by the frame member 13, and the rear lens group 12 is held by the frame member 14. Further, the image sensor 15 is held by the frame member 16.
  • the oblique objective optical system 17 and the oblique objective optical system 18 are oblique objective optical systems that perform forward viewing.
  • the optical axis of the front lens group and the optical axis of the rear lens group intersect with each other by two reflections on the prism.
  • the perspective objective optical system 17 uses two frame members, and the perspective objective optical system 18 uses three frame members.
  • JP 51-62053 A Japanese Patent No. 3385090 Japanese Patent No. 3574484 Japanese Patent No. 4439184 Japanese Patent No. 4814746
  • the perspective objective optical system disclosed in Patent Document 1 has a large optical system as a whole and has insufficient optical performance. Therefore, the perspective objective optical system disclosed in Patent Document 1 can be applied to an imaging device such as a CCD having a small number of pixels, that is, a perspective objective optical system corresponding to high performance and downsizing. It cannot be applied to the system.
  • the perspective objective optical system disclosed in Patent Document 2 a glass material having a low refractive index is used for each of the negative lens and the prism of the first lens group in order to correct chromatic aberration.
  • the air equivalent length on the object side is particularly longer than the aperture stop.
  • the outer diameter of the negative lens and the outer diameter of the prism are increased. Therefore, the perspective objective optical system disclosed in Patent Document 2 cannot be applied to a perspective objective optical system corresponding to high performance and downsizing.
  • the perspective objective optical system disclosed in Patent Document 3 since the back focus is long, the entire optical system becomes large. Further, since the focal length of the negative lens in the front group is short, the negative refractive power of the front group is large. However, since the back focus is long, the focal length of the cemented lens is long. Thus, the optical performance is not sufficient because the balance of refractive power in the entire optical system is poor. Therefore, the perspective objective optical system disclosed in Patent Document 3 cannot be applied to a perspective objective optical system corresponding to high performance and downsizing.
  • the focal length of the first group is short (the negative refractive power of the first group is large).
  • the focal length of the second group is long (the positive refractive power of the second group is small).
  • the balance between the negative refractive power and the positive refractive power is lost, field curvature and astigmatism occur.
  • the perspective objective optical system disclosed in Patent Document 5 since the image height is high, the outer diameter of the lens of the second group is also large. Therefore, the perspective objective optical system disclosed in Patent Document 5 cannot be applied to a perspective objective optical system corresponding to high performance and downsizing.
  • the frame member 13 and the frame member 14 are connected by the fitting part 13a and the fitting part 14a.
  • the frame member 13 and the frame member 14 are each held by a jig. And after fixing the relative position of both, it fixes.
  • the frame member 13 and the frame member 14 are also shortened. If the frame member 13 and the frame member 14 become too short, the jig holding the frame member 13 and the jig holding the frame member 14 interfere with each other. Therefore, it becomes impossible to assemble the perspective objective optical system 9.
  • the perspective objective optical system 9 cannot be assembled with high accuracy.
  • the frame member 14 and the frame member 16 are connected by the fitting part 14b and the fitting part 16a.
  • the above-described problem also occurs with respect to the frame member 14 and the frame member 16.
  • the perspective objective optical system 9 is incorporated into the endoscope distal end portion through the fitting portion 13 b of the frame member 13. If the perspective objective optical system 9 is downsized, it is difficult to ensure a sufficient length of the fitting portion 13b. In this case, it becomes difficult to keep the frame member 13 in a predetermined state with respect to the distal end portion of the endoscope. Therefore, the perspective objective optical system 9 cannot be attached to the endoscope distal end with high accuracy.
  • the perspective objective optical system 17 uses two frame members, and the perspective objective optical system 18 uses three frame members. Therefore, the above-described problems occur in these perspective objective optical systems.
  • the present invention has been made in view of such problems, and provides a high-performance and compact perspective objective optical system that can be assembled and attached to an endoscope distal end with high accuracy and ease. With the goal.
  • the present invention provides a perspective endoscope having a high-quality image and having a thinned tip.
  • the perspective objective optical system of the present invention includes: In order from the object side, the front lens group including a negative lens, an optical path conversion element, an aperture stop, and a rear lens group having a positive refractive power,
  • the rear lens group includes a positive lens and a cemented lens having a positive refractive power.
  • the cemented lens is composed of a positive lens and a negative lens in order from the object side.
  • f F is the focal length of the front lens group
  • f R is the focal length of the rear lens group
  • f is the focal length of the entire oblique objective optical system, It is.
  • the perspective endoscope of the present invention is The above-mentioned perspective objective optical system is provided.
  • assembly and attachment to the distal end portion of the endoscope can be easily performed with high accuracy, and a high-performance and compact perspective optical system can be realized.
  • FIG. 6 is a diagram illustrating a cross-sectional configuration of a perspective objective optical system according to Example 1, and an aberration diagram illustrating spherical aberration (SA), astigmatism (AS), distortion (DT), and lateral chromatic aberration (CC).
  • SA spherical aberration
  • AS astigmatism
  • DT distortion
  • CC lateral chromatic aberration
  • FIG. 6 is a diagram illustrating a cross-sectional configuration of a perspective objective optical system according to Example 2, and aberration diagrams illustrating spherical aberration (SA), astigmatism (AS), distortion (DT), and lateral chromatic aberration (CC).
  • SA spherical aberration
  • AS astigmatism
  • DT distortion
  • CC lateral chromatic aberration
  • FIG. 6 is a diagram illustrating a cross-sectional configuration of a perspective objective optical system according to Example 4 and aberration diagrams illustrating spherical aberration (SA), astigmatism (AS), distortion (DT), and lateral chromatic aberration (CC).
  • FIG. 10 is a diagram illustrating a cross-sectional configuration of a perspective objective optical system according to Example 5, and aberration diagrams illustrating spherical aberration (SA), astigmatism (AS), distortion (DT), and lateral chromatic aberration (CC).
  • SA spherical aberration
  • AS astigmatism
  • DT distortion
  • CC lateral chromatic aberration
  • FIG. 10 is a diagram illustrating a cross-sectional configuration of a perspective objective optical system according to Example 6, and aberration diagrams illustrating spherical aberration (SA), astigmatism (AS), distortion (DT), and lateral chromatic aberration (CC).
  • SA spherical aberration
  • AS astigmatism
  • DT distortion
  • CC lateral chromatic aberration
  • FIG. 10 is a diagram illustrating a cross-sectional configuration of a perspective objective optical system according to Example 8 and aberration diagrams illustrating spherical aberration (SA), astigmatism (AS), distortion (DT), and lateral chromatic aberration (CC).
  • SA spherical aberration
  • AS astigmatism
  • DT distortion
  • CC lateral chromatic aberration
  • FIG. 10 is a diagram illustrating a cross-sectional configuration of a perspective objective optical system according to Example 10 and aberration diagrams illustrating spherical aberration (SA), astigmatism (AS), distortion (DT), and lateral chromatic aberration (CC).
  • SA spherical aberration
  • AS astigmatism
  • DT distortion
  • CC lateral chromatic aberration
  • FIG. 14 is a diagram illustrating a cross-sectional configuration of a perspective objective optical system according to Example 12 and aberration diagrams illustrating spherical aberration (SA), astigmatism (AS), distortion (DT), and lateral chromatic aberration (CC).
  • SA spherical aberration
  • AS astigmatism
  • DT distortion
  • CC lateral chromatic aberration
  • FIG. 18 is a diagram illustrating a cross-sectional configuration of a perspective objective optical system according to Example 14 and aberration diagrams illustrating spherical aberration (SA), astigmatism (AS), distortion (DT), and lateral chromatic aberration (CC).
  • SA spherical aberration
  • AS astigmatism
  • DT distortion
  • CC lateral chromatic aberration
  • the perspective objective optical system of the present embodiment is composed of, in order from the object side, a front lens group including a negative lens, an optical path conversion element, an aperture stop, and a rear lens group having a positive refractive power.
  • the rear lens group includes a positive lens and a cemented lens having a positive refractive power, and the cemented lens includes a positive lens and a negative lens in order from the object side.
  • the optical path conversion element By arranging the optical path conversion element in the vicinity of the aperture stop, that is, on the object side of the brightness stop or the image side of the aperture stop, the light beam height in the optical path conversion element can be kept low. As a result, the size of the optical path conversion element can be reduced.
  • the distance from the aperture stop to the image plane becomes longer by at least the glass path length of the optical path conversion element. If it does so, the light ray radiate
  • focus adjustment is performed when assembling the perspective objective optical system. For this reason, if an attempt is made to satisfy the oblique incident characteristics of the image sensor, the interval necessary for focus adjustment is insufficient. Further, since the light beam is forcibly bent in accordance with the oblique incidence characteristic, an aberration occurs. As a result, the optical performance is significantly deteriorated.
  • the optical path conversion element is arranged on the object side of the aperture stop. Therefore, since the distance from the aperture stop to the image plane can be shortened, it is relatively easy to set the angle of the light beam emitted from the oblique objective optical system to an angle that satisfies the oblique incidence characteristics of the image sensor.
  • the glass path length is longer on the object side than the aperture stop. Therefore, the length of the frame member that holds the front lens group can be appropriately ensured. As a result, assembly of the perspective objective optical system and attachment of the perspective objective optical system to the distal end portion of the endoscope can be easily performed with high accuracy.
  • the cemented lens is preferably composed of a positive lens and a negative lens in order from the object side. By doing in this way, a perspective objective optical system can be reduced in size.
  • the angle of the light beam emitted from the oblique objective optical system can be set to an angle that satisfies the oblique incident characteristics of the image sensor.
  • the cemented lens is composed of a negative lens and a positive lens in this order from the object side, the height of the light beam at the cemented lens increases, and the outer diameter of the lens increases. Therefore, the processability of the lens is deteriorated. Also, the outer diameter of the entire perspective objective optical system becomes large.
  • the light beam emitted from the oblique objective optical system becomes almost perpendicular to the light receiving surface of the image sensor.
  • Forcing the angle to satisfy the oblique incidence characteristic causes aberrations because the light rays are greatly bent at the cemented lens surface. Therefore, the optical performance is deteriorated.
  • the perspective objective optical system of the present embodiment has the above configuration and satisfies the following conditional expressions (1) and (2). -2.0 ⁇ f F /f ⁇ -1.3 (1) 1.7 ⁇ f R /f ⁇ 2.7 (2) here, f F is the focal length of the front lens group, f R is the focal length of the rear lens group, f is the focal length of the entire oblique objective optical system, It is.
  • Conditional expression (1) is a conditional expression that defines the focal length of the front lens group.
  • conditional expression (1) When the lower limit value of conditional expression (1) is not reached, the refractive power of the front lens group becomes small, so the angle of view of the perspective objective optical system becomes small. If a large angle of view is to be secured in this state, the distance from the negative lens in the front lens group (hereinafter referred to as “front negative lens”) to the aperture stop becomes long. As a result, the height of the light beam from the front negative lens to the aperture stop becomes high, which increases the size of the front negative lens and the size of the entire optical system.
  • conditional expression (1) If the upper limit value of conditional expression (1) is exceeded, the refractive power of the front lens unit increases, so the angle of view of the perspective objective optical system increases. As the angle of view increases, the height of the light beam passing through the lens increases, and the outer diameter of the lens increases. Furthermore, the peripheral portion of the observation image becomes dark as the angle of view increases. In order to brighten the peripheral portion of the image, it is necessary to further brighten the illumination light. However, this would increase the size of the illumination optical system. Neither is preferred for reducing the diameter of an endoscope.
  • the refractive power of the front lens group increases, the radius of curvature of the front negative lens decreases, making it difficult to process the lens. Furthermore, since the refractive power of the front negative lens is increased, the deterioration of the optical performance is increased particularly when the lens is decentered. As a result, it becomes difficult to realize a perspective objective optical system having stable optical performance.
  • Conditional expression (2) is a conditional expression that defines the focal length of the rear lens group.
  • conditional expression (2) If the lower limit value of conditional expression (2) is not reached, the refractive power of the rear lens unit increases, and the image position becomes too close to the rear lens unit. As a result, the interval necessary for focus adjustment becomes narrow, and the interval necessary for focus adjustment is insufficient. For this reason, the depth on the far point side is shallower than the originally required depth.
  • the refractive power of the rear lens group increases, the refractive power of each lens constituting the rear lens group also increases. In this case, since the radius of curvature of each lens becomes small, it becomes difficult to process the lens.
  • conditional expression (2) If the upper limit value of conditional expression (2) is exceeded, the refractive power of the rear lens group becomes small, so that the image position is too far from the rear lens group. In this case, since the glass path length from the aperture stop to the image position becomes long, the entire optical system becomes large.
  • conditional expression (1) and conditional expression (2) in the perspective objective optical system according to this embodiment, the balance between the refractive power of the front lens group and the refractive power of the rear lens group is optimized. Can do. As a result, a perspective objective optical system in which various aberrations are favorably corrected can be realized.
  • conditional expression (1 ′) instead of conditional expression (1).
  • conditional expression (2) It is preferable to satisfy the following conditional expression (2 ′) instead of conditional expression (2). 1.8 ⁇ f R /f ⁇ 2.5 (2 ′)
  • the perspective objective optical system of the present embodiment satisfies the following conditional expression (3). 0.63 ⁇
  • Conditional expression (3) is a conditional expression that defines the ratio of the focal length of the front lens group and the focal length of the rear lens group.
  • the focal length of the front lens unit is shortened (the refractive power of the front lens unit is increased). Therefore, the angle of view of the perspective objective optical system is increased. As the angle of view increases, the height of the light beam passing through the lens increases, and the outer diameter of the lens increases. Furthermore, the peripheral portion of the observation image becomes dark as the angle of view increases. In order to brighten the peripheral portion of the image, it is necessary to further brighten the illumination light. However, this would increase the size of the illumination optical system. Neither is preferred for reducing the diameter of an endoscope.
  • the refractive power of the front negative lens is greater than the positive refractive power of the rear lens group. Therefore, the aberration that is affected by the negative refractive power cannot be sufficiently corrected by the rear lens group. As a result, field curvature occurs in the positive direction.
  • the balance between the refractive power of the front lens group and the refractive power of the rear lens group becomes worse.
  • the amount of astigmatism increases, and in particular, the image plane in the meridian direction is greatly tilted in the positive direction. Therefore, when the lens is decentered, one-side blur tends to occur in the image. In particular, there is a risk that the peripheral portion of the image will be significantly blurred during near-point observation.
  • the refractive power of the front negative lens is smaller than the positive refractive power of the rear lens group. For this reason, correction by the rear lens unit becomes excessive for aberrations that are affected by negative refractive power. As a result, a large curvature of field occurs in the negative direction.
  • the balance between the refractive power of the front lens group and the refractive power of the rear lens group becomes worse.
  • the image plane in the meridian direction is particularly inclined in the negative direction. Therefore, when the lens is decentered, one-side blur tends to occur in the image.
  • the peripheral portion of the image may be significantly blurred during far-point observation.
  • the perspective objective optical system of this embodiment satisfies the following conditional expressions (4) and (5).
  • D1 is the air equivalent length from the image side surface of the negative lens of the front lens group to the aperture stop
  • D2 is the air equivalent length from the image side surface to the image surface of the final lens in the rear lens group
  • f is the focal length of the entire oblique objective optical system, It is.
  • Conditional expression (4) is a conditional expression that defines the air-converted length from the image side surface of the negative lens of the front lens group to the aperture stop.
  • conditional expression (4) If the lower limit value of conditional expression (4) is not reached, it is difficult to ensure a sufficient space for arranging the optical path conversion element having the optimum outer diameter shape. For this reason, the optical path conversion element causes light beam shifting. Moreover, there is a possibility that flare may occur in an image when light rays enter other than the optical surface of the optical path conversion element.
  • the frame member cannot be stably held on the jig for assembly. Therefore, it becomes difficult to assemble the perspective objective optical system and adjust the focus with high accuracy. Furthermore, it becomes difficult to attach and fix the oblique objective optical system to the distal end portion of the endoscope with high accuracy.
  • conditional expression (4) If the upper limit value of conditional expression (4) is exceeded, a sufficient space for arranging the optical path conversion element can be secured, but the glass path length from the front negative lens to the aperture stop becomes too long. In this case, the height of the light beam in the front negative lens increases, so the outer diameter of the front negative lens increases. Along with this, the perspective objective optical system becomes larger. Furthermore, as the perspective objective optical system increases in size, the outer diameter of the endoscope on which it is mounted also increases.
  • Conditional expression (5) is a conditional expression that defines the air-converted length from the image side surface to the image surface of the final lens in the rear lens group.
  • the final lens means a lens having refractive power. Therefore, a parallel plate filter such as a color filter or a powerless lens is not the final lens.
  • conditional expression (5) If the lower limit of conditional expression (5) is not reached, the distance from the final lens to the image plane becomes too narrow. In this case, since the distance between the imaging element and the perspective objective optical system becomes too narrow, sufficient focus adjustment cannot be performed when the perspective objective optical system is assembled. For this reason, the depth on the far point side is shallower than the originally required depth.
  • the upper limit of conditional expression (5) is exceeded, a sufficient distance from the final lens to the image plane can be secured, so that the focus adjustment during assembly of the perspective objective optical system can be performed.
  • the position of the image sensor is too far from the perspective objective optical system.
  • imaging system the oblique objective optical system and the imaging element (hereinafter referred to as “imaging system”) are likely to interfere with other members. In order to avoid this interference, it is necessary to provide a clearance around the imaging system in the endoscope. If it does so, the whole endoscope front-end
  • conditional expression (4 ′) instead of conditional expression (4).
  • conditional expression (4) 2.4 ⁇ D1 / f ⁇ 4.2 (4 ′)
  • conditional expression (5 ′) instead of conditional expression (5). 1.1 ⁇ D2 / f ⁇ 1.6 (5 ′)
  • the perspective objective optical system of this embodiment satisfies the following conditional expression (6).
  • D1 is the air equivalent length from the image side surface of the negative lens of the front lens group to the aperture stop
  • D2 is the air equivalent length from the image side surface to the image surface of the final lens in the rear lens group
  • Conditional expression (6) is the ratio of the air-converted length from the image side surface of the negative lens in the front lens unit to the aperture stop and the air-converted length from the image side surface of the final lens in the rear lens unit to the image surface. It is a defined conditional expression.
  • conditional expression (6) If the upper limit value of conditional expression (6) is exceeded, the frame member becomes larger. In particular, since the frame member that holds the front lens group is increased in size, the outer diameter of the endoscope distal end is increased.
  • the perspective objective optical system of this embodiment satisfies the following conditional expression (7).
  • f 2 is the focal length of the positive lens in the rear lens group
  • f 3 is the focal length of the cemented lens in the rear lens group
  • Conditional expression (7) is a conditional expression that defines the focal length of the positive lens in the rear lens group and the focal length of the cemented lens in the rear lens group. By satisfying conditional expression (7), the balance between the refractive power of the positive lens and the refractive power of the cemented lens can be optimized.
  • the focal length of the cemented lens is shortened, so that the positive refractive power in the rear lens group is increased.
  • the image position is too close to the rear lens group. . Therefore, the interval necessary for focus adjustment is insufficient.
  • the depth on the far point side becomes shallower than the originally required depth.
  • the optical performance is degraded.
  • the balance between the refractive power of the entire positive lens and the refractive power of the entire negative lens is lost.
  • axial chromatic aberration and lateral chromatic aberration are generated. Therefore, the optical performance is deteriorated.
  • conditional expression (7) If the upper limit value of conditional expression (7) is exceeded, the focal length of the cemented lens becomes longer, so the positive refractive power in the rear lens group becomes smaller. In this case, the image position is too far from the rear lens group. Therefore, the total length of the optical system becomes long. In addition, since the amount of coma generated at the periphery of the image is increased, the optical performance is degraded.
  • the balance between the refractive power of the entire positive lens and the refractive power of the entire negative lens is lost.
  • axial chromatic aberration and lateral chromatic aberration are generated. Therefore, the optical performance is deteriorated.
  • the perspective objective optical system of this embodiment satisfies the following conditional expression (8).
  • R c is the radius of curvature of the cemented surface of the cemented lens in the rear lens group
  • f is the focal length of the entire oblique objective optical system, It is.
  • R c is defined as an absolute value, but the value of R c is preferably a negative value.
  • the perspective objective optical system of this embodiment satisfies the following conditional expression (9). -17 ° ⁇ TW ⁇ 0 ° (9) here, TW is the light incident angle on the image plane at the maximum image height, It is.
  • Satisfying conditional expression (9) makes it possible to keep the light beam height in the rear lens group low. Therefore, the outer diameter of the lens in the rear lens group can be reduced. In addition, the rear lens group can be reduced in size with the frame member included.
  • TW is an angle formed between a principal ray reaching the maximum image height and an axis parallel to the optical axis. The sign of the angle is negative when the chief ray that reaches the maximum image height enters the optical axis gradually away from the optical axis. TW is an angle when the medium is in the air.
  • conditional expression (9 ′) ⁇ 12 ° ⁇ TW ⁇ ⁇ 5 ° (9 ')
  • the optical path conversion element is preferably a prism or a mirror.
  • a high refractive index glass material can be used for the optical path conversion element.
  • the optical path conversion element is arranged on the object side of the aperture stop.
  • the length of the frame member that holds the front lens group can be appropriately secured.
  • the height of the light beam is particularly high in the front negative lens, so the outer diameter of the front negative lens tends to increase.
  • the optical path conversion element it is preferable to use a high refractive index glass material for the optical path conversion element. By doing in this way, since the air conversion length of an optical path conversion element can be shortened, the light ray height in a front negative lens can be suppressed low.
  • a low dispersion glass material can be used for the positive lens of the cemented lens, and a high dispersion glass material can be used for the negative lens of the cemented lens.
  • a low dispersion glass material for the positive lens of the cemented lens and a high dispersion glass material for the negative lens of the cemented lens are preferable to use.
  • a glass material having anomalous dispersion is preferably used for the negative lens of the cemented lens. In this way, chromatic aberration can be corrected satisfactorily. Further, various aberrations in the entire oblique objective optical system can be balanced.
  • the angle of view of the perspective objective optical system is mainly determined by the refractive power of the front negative lens. Since an optical path conversion element having a long glass path length is disposed between the front negative lens and the aperture stop, the light beam height at the front negative lens is increased. For this reason, the outer diameter of the negative lens increases and the objective optical system also increases in size. However, since the radius of curvature of the front negative lens is increased, even if the front negative lens is decentered, one-sided blur or the like is less likely to occur, and the optical performance is less likely to be deteriorated. For this reason, in consideration of not only the lens outer diameter but also the effect on the optical performance due to the lens decentering, it is necessary to optimize the configuration on the object side from the aperture stop.
  • the perspective endoscope of the present embodiment is characterized by including the above-described perspective objective optical system.
  • the perspective objective optical system of the present embodiment is a small and high-performance perspective objective optical system. Therefore, by providing such a perspective objective optical system, a high-quality image can be obtained, and a perspective endoscope having a thinned tip can be realized.
  • the perspective objective optical system of the present embodiment can be used for an endoscope apparatus.
  • the endoscope apparatus includes at least the perspective objective optical system of the present embodiment and an image sensor.
  • the optical path conversion element is shown as a developed view of a prism. Therefore, the optical path conversion element is drawn as a parallel plane plate.
  • FIG. 6 shows an example of a prism that is not expanded.
  • FIG. 6A is a lens cross-sectional view when the prism is drawn without being developed.
  • the perspective objective optical system of Example 1 is illustrated as the perspective objective optical system of the present example.
  • the perspective objective optical system of the present embodiment has a front lens group GF and a rear lens group GR disposed via a prism P, and an aperture stop S is disposed between the prism P and the rear lens group GR. Has been.
  • the front lens group GF is disposed on the object side of the prism P, and the rear lens group GR is disposed on the image side of the prism P.
  • the front lens group GF has a negative refractive power and includes a lens L1 having a negative refractive power.
  • the rear lens group GR has a positive refractive power, and has a positive refractive power formed by sequentially joining a lens L2 having a positive refractive power, a lens L3 having a positive refractive power, and a lens L4 having a negative refractive power. It consists of a lens.
  • the prism P drawn as a parallel plate is configured as a single reflection type prism, as shown in FIG. 6A, a side-view objective optical system capable of 90-degree side observation can be configured. it can. Further, if the reflecting surface of the prism is set to an angle other than 45 degrees, an objective optical system such as a front view and a rear view other than 45 degrees can be configured. Further, if it is configured as a twice-reflection type prism, a 45 ° forward-view objective optical system can also be configured.
  • the prism P can be composed of a plurality of prisms.
  • FIG. 6B illustrates a configuration in which the two prisms can be viewed from the side
  • FIG. 6C illustrates a configuration in which the two prisms can be viewed from the front.
  • a high refractive index glass material having a refractive index of 1.8 or more for the glass material of the prism P.
  • the glass material of the negative lens L1 may be sapphire. Since sapphire is a very hard material, it is resistant to external impacts. Therefore, the lens surface on the object side is hardly damaged. By using sapphire, reflection of scratches on an image and occurrence of flare due to scratches are less likely to occur. Note that the glass material of the negative lens is not limited to sapphire. If a crystal material with high hardness is used for the negative lens L1, the surface of the lens is hardly damaged.
  • both positive lenses have a biconvex shape. Since the refractive index of a low dispersion glass material is low, if the low dispersion glass material is used for a positive lens, the radius of curvature of the lens surface becomes small. Therefore, the problem that the edge thickness of the lens cannot be sufficiently secured and the problem that the lens outer diameter having a margin with respect to the effective aperture cannot be secured are likely to occur. Therefore, in consideration of the processability of the lens, it is preferable that the radius of curvature of the positive lens is not too small. For this reason, a high refractive index glass material having a refractive index of 1.7 or higher is preferably used for at least one of the positive lens L2 and the positive lens L3.
  • the object side surface and the image side surface are surfaces having the same absolute value of the radius of curvature (hereinafter referred to as “equal R surface”). In this way, it is easy to assemble because there is no need to determine the front and back of the lens.
  • the absolute value of the curvature radius of the object side surface may be larger than the absolute value of the curvature radius of the image side surface. In this way, aberration correction can be easily performed.
  • a low dispersion glass material having a large Abbe number is preferably used for the positive lens L3 constituting the cemented lens.
  • the cemented lens by arranging the cemented lens at a position close to the image plane, the height of the light beam passing through the cemented lens becomes high. Since the cemented lens is positioned at a position where the light beam height is high, the lateral chromatic aberration can be favorably corrected. Thus, disposing the cemented lens at a position close to the image plane is particularly effective for correcting lateral chromatic aberration.
  • the parallel plate other than the prism provided in the perspective objective optical system of the present embodiment is, for example, an infrared cut filter or a color temperature conversion filter. These filters are used for sensitivity correction of an image sensor such as a CCD.
  • a laser cut filter or a special function filter may be arranged in the perspective objective optical system.
  • the laser cut filter include a filter for cutting laser light such as a YAG laser and a semiconductor laser.
  • the special function filter for example, there is a notch filter that cuts light in a specific wavelength range.
  • an absorption type filter, a reflection type filter, or a composite type thereof may be used.
  • an antireflection film may be provided on the surface of the optical filter.
  • an interference film having infrared cut characteristics or laser light cut characteristics can be provided on the transmission surface of the prism.
  • the parallel plate filter disposed on the image plane side of the perspective objective optical system of the present embodiment is a glass lid and a cover glass used for the image sensor.
  • the image sensor is fixed in the frame member by holding the side surface and the surface of the cover glass with the frame member.
  • the filter F1 close to the negative lens L1
  • the volume of the air layer formed on the image plane side of the negative lens L1 can be reduced.
  • the influence of fogging due to condensation on the lens surface can be reduced.
  • the negative lens L1 and the filter F1 may be joined, and both may be hermetically sealed with solder or the like. By doing in this way, generation
  • the number of lenses of the perspective objective optical system of this embodiment is as small as four, the imaging performance is good. In this way, since the objective optical system can be configured with a small number of lenses, the cost can be reduced.
  • the air interval is narrower than that of the conventional perspective objective optical system, so the entire optical system is small.
  • the horizontal axis represents the amount of aberration.
  • the unit of aberration is mm.
  • the unit of aberration is%. IH is the image height, the unit is mm, and FNO is the F number.
  • the unit of the wavelength of the aberration curve is nm.
  • Example 1 A perspective objective optical system according to Example 1 will be described.
  • 7A and 7B are diagrams and aberration diagrams showing the cross-sectional configuration of the perspective objective optical system according to Example 1.
  • FIG. 7A is a lens cross section
  • FIG. 7B is spherical aberration (SA)
  • FIG. (AS) and (d) show distortion aberration (DT)
  • CC lateral chromatic aberration
  • the oblique objective optical system includes, in order from the object side, a front lens group GF having a negative refractive power, an optical path conversion element P, an aperture stop S, and a positive refractive power.
  • Rear lens group GR Rear lens group
  • the front lens group GF includes a plano-concave negative lens L1 having a flat object side.
  • a filter F1 is disposed in the front lens group GF.
  • the filter F1 is disposed between the plano-concave negative lens L1 and the optical path conversion element P.
  • the optical path conversion element P is disposed between the front lens group GF and the rear lens group GR.
  • the optical path conversion element P is a prism.
  • a high refractive index glass material having a refractive index of 1.8 or more is used for the prism.
  • the brightness stop S is disposed between the optical path conversion element P and the rear lens group GR. More specifically, the aperture stop S is provided on the image side surface of the optical path conversion element P.
  • the rear lens group GR includes a biconvex positive lens L2, a biconvex positive lens L3, and a negative meniscus lens L4 having a convex surface facing the image side.
  • the biconvex positive lens L3 and the negative meniscus lens L4 form a cemented lens having a positive refractive power. Both surfaces of the biconvex positive lens L2 are equal R surfaces.
  • a filter F2, a glass lid GL, and a cover glass CG are disposed in the rear lens group GR. The filter F2 is disposed between the biconvex positive lens L2 and the cemented lens.
  • FIG. 8 is a diagram showing a cross-sectional configuration of the perspective objective optical system according to Example 2 and aberration diagrams, where (a) is a lens cross section, (b) is spherical aberration (SA), and (c) is astigmatism. (AS) and (d) show distortion aberration (DT), and (e) shows lateral chromatic aberration (CC).
  • SA spherical aberration
  • DT distortion aberration
  • CC lateral chromatic aberration
  • the perspective objective optical system of Example 2 includes, in order from the object side, a front lens group GF having a negative refractive power, an optical path conversion element P, an aperture stop S, and a positive refractive power.
  • Rear lens group GR Rear lens group
  • the front lens group GF includes a plano-concave negative lens L1 having a flat object side.
  • a filter F1 is disposed in the front lens group GF.
  • the filter F1 is disposed between the plano-concave negative lens L1 and the optical path conversion element P.
  • the optical path conversion element P is disposed between the front lens group GF and the rear lens group GR.
  • the optical path conversion element P is a prism.
  • a high refractive index glass material having a refractive index of 1.8 or more is used for the prism.
  • the brightness stop S is disposed between the optical path conversion element P and the rear lens group GR. More specifically, the aperture stop S is provided on the image side surface of the optical path conversion element P.
  • the rear lens group GR includes a biconvex positive lens L2, a biconvex positive lens L3, and a negative meniscus lens L4 having a convex surface facing the image side.
  • the biconvex positive lens L3 and the negative meniscus lens L4 form a cemented lens having a positive refractive power.
  • the absolute value of the radius of curvature of the object side surface of the biconvex positive lens L2 is larger than the absolute value of the radius of curvature of the image side surface.
  • a filter F2, a glass lid GL, and a cover glass CG are disposed in the rear lens group GR.
  • the filter F2 is disposed between the biconvex positive lens L2 and the cemented lens.
  • FIG. 9 is a diagram illustrating a cross-sectional configuration of the perspective objective optical system according to Example 3 and aberration diagrams, where (a) is a lens cross section, (b) is spherical aberration (SA), and (c) is astigmatism. (AS) and (d) show distortion aberration (DT), and (e) shows lateral chromatic aberration (CC).
  • SA spherical aberration
  • DT distortion aberration
  • CC lateral chromatic aberration
  • the perspective objective optical system according to the third embodiment includes, in order from the object side, a front lens group GF having a negative refractive power, an optical path conversion element P, an aperture stop S, and a positive refractive power.
  • Rear lens group GR Rear lens group
  • the front lens group GF includes a plano-concave negative lens L1 having a flat object side.
  • a filter F1 is disposed in the front lens group GF.
  • the filter F1 is disposed between the plano-concave negative lens L1 and the optical path conversion element P.
  • the optical path conversion element P is disposed between the front lens group GF and the rear lens group GR.
  • the optical path conversion element P is a prism.
  • a high refractive index glass material having a refractive index of 1.8 or more is used for the prism.
  • the brightness stop S is disposed between the optical path conversion element P and the rear lens group GR. More specifically, the aperture stop S is provided on the image side surface of the optical path conversion element P.
  • the rear lens group GR includes a biconvex positive lens L2, a biconvex positive lens L3, and a negative meniscus lens L4 having a convex surface facing the image side.
  • the biconvex positive lens L3 and the negative meniscus lens L4 form a cemented lens having a positive refractive power. Both surfaces of the biconvex positive lens L2 are equal R surfaces.
  • a filter F2, a glass lid GL, and a cover glass CG are disposed in the rear lens group GR. The filter F2 is disposed between the biconvex positive lens L2 and the cemented lens.
  • FIG. 10A and 10B are a diagram illustrating a cross-sectional configuration of the perspective objective optical system according to Example 4 and aberration diagrams, in which FIG. 10A is a lens cross section, FIG. 10B is spherical aberration (SA), and FIG. (AS) and (d) show distortion aberration (DT), and (e) shows lateral chromatic aberration (CC).
  • SA spherical aberration
  • AS spherical aberration
  • DT distortion aberration
  • CC lateral chromatic aberration
  • the perspective objective optical system of Example 4 includes, in order from the object side, a front lens group GF having a negative refractive power, an optical path conversion element P, an aperture stop S, and a positive refractive power.
  • Rear lens group GR Rear lens group
  • the front lens group GF includes a plano-concave negative lens L1 having a flat object side.
  • a filter F1 is disposed in the front lens group GF.
  • the filter F1 is disposed between the plano-concave negative lens L1 and the optical path conversion element P.
  • the optical path conversion element P is disposed between the front lens group GF and the rear lens group GR.
  • the optical path conversion element P is a prism.
  • a high refractive index glass material having a refractive index of 1.8 or more is used for the prism.
  • the brightness stop S is disposed between the optical path conversion element P and the rear lens group GR. More specifically, the aperture stop S is provided on the image side surface of the optical path conversion element P.
  • the rear lens group GR includes a biconvex positive lens L2, a biconvex positive lens L3, and a negative meniscus lens L4 having a convex surface facing the image side.
  • the biconvex positive lens L3 and the negative meniscus lens L4 form a cemented lens having a positive refractive power. Both surfaces of the biconvex positive lens L2 are equal R surfaces.
  • a filter F2, a glass lid GL, and a cover glass CG are disposed in the rear lens group GR. The filter F2 is disposed between the biconvex positive lens L2 and the cemented lens.
  • FIG. 11 is a diagram illustrating a cross-sectional configuration of the perspective objective optical system according to Example 5 and aberration diagrams, where (a) is a lens cross section, (b) is spherical aberration (SA), and (c) is astigmatism. (AS) and (d) show distortion aberration (DT), and (e) shows lateral chromatic aberration (CC).
  • SA spherical aberration
  • DT distortion aberration
  • CC lateral chromatic aberration
  • the oblique objective optical system of Example 5 includes, in order from the object side, a front lens group GF having a negative refractive power, an optical path conversion element P, an aperture stop S, and a positive refractive power.
  • Rear lens group GR Rear lens group
  • the front lens group GF includes a plano-concave negative lens L1 having a flat object side.
  • a filter F1 is disposed in the front lens group GF.
  • the filter F1 is disposed between the plano-concave negative lens L1 and the optical path conversion element P.
  • the optical path conversion element P is disposed between the front lens group GF and the rear lens group GR.
  • the optical path conversion element P is a prism.
  • a high refractive index glass material having a refractive index of 1.8 or more is used for the prism.
  • the brightness stop S is disposed between the optical path conversion element P and the rear lens group GR. More specifically, the aperture stop S is provided on the image side surface of the optical path conversion element P.
  • the rear lens group GR includes a biconvex positive lens L2, a biconvex positive lens L3, and a negative meniscus lens L4 having a convex surface facing the image side.
  • the biconvex positive lens L3 and the negative meniscus lens L4 form a cemented lens having a positive refractive power. Both surfaces of the biconvex positive lens L2 are equal R surfaces.
  • a filter F2, a glass lid GL, and a cover glass CG are disposed in the rear lens group GR. The filter F2 is disposed between the biconvex positive lens L2 and the cemented lens.
  • FIG. 12 is a diagram showing a cross-sectional configuration of a perspective objective optical system according to Example 6 and aberration diagrams, where (a) is a lens cross section, (b) is spherical aberration (SA), and (c) is astigmatism. (AS) and (d) show distortion aberration (DT), and (e) shows lateral chromatic aberration (CC).
  • SA spherical aberration
  • DT distortion aberration
  • CC lateral chromatic aberration
  • the oblique objective optical system of Example 6 includes, in order from the object side, a front lens group GF having a negative refractive power, an optical path conversion element P, an aperture stop S, and a positive refractive power.
  • Rear lens group GR Rear lens group
  • the front lens group GF includes a plano-concave negative lens L1 having a flat object side.
  • a filter F1 is disposed in the front lens group GF.
  • the filter F1 is disposed between the plano-concave negative lens L1 and the optical path conversion element P.
  • the optical path conversion element P is disposed between the front lens group GF and the rear lens group GR.
  • the optical path conversion element P is a prism.
  • a high refractive index glass material having a refractive index of 1.8 or more is used for the prism.
  • the brightness stop S is disposed between the optical path conversion element P and the rear lens group GR. More specifically, the aperture stop S is provided on the image side surface of the optical path conversion element P.
  • the rear lens group GR includes a biconvex positive lens L2, a biconvex positive lens L3, and a negative meniscus lens L4 having a convex surface facing the image side.
  • the biconvex positive lens L3 and the negative meniscus lens L4 form a cemented lens having a positive refractive power. Both surfaces of the biconvex positive lens L2 are equal R surfaces.
  • a filter F2, a glass lid GL, and a cover glass CG are disposed in the rear lens group GR. The filter F2 is disposed between the biconvex positive lens L2 and the cemented lens.
  • FIG. 13 is a diagram showing a cross-sectional configuration of a perspective objective optical system according to Example 7 and aberration diagrams, where (a) is a lens cross section, (b) is spherical aberration (SA), and (c) is astigmatism. (AS) and (d) show distortion aberration (DT), and (e) shows lateral chromatic aberration (CC).
  • SA spherical aberration
  • DT distortion aberration
  • CC lateral chromatic aberration
  • the perspective objective optical system of Example 7 includes, in order from the object side, a front lens group GF having a negative refractive power, an optical path conversion element P, an aperture stop S, and a positive refractive power.
  • Rear lens group GR Rear lens group
  • the front lens group GF includes a plano-concave negative lens L1 having a flat object side.
  • a filter F1 is disposed in the front lens group GF.
  • the filter F1 is disposed between the plano-concave negative lens L1 and the optical path conversion element P.
  • the optical path conversion element P is disposed between the front lens group GF and the rear lens group GR.
  • the optical path conversion element P is a prism.
  • a high refractive index glass material having a refractive index of 1.8 or more is used for the prism.
  • the brightness stop S is disposed between the optical path conversion element P and the rear lens group GR. More specifically, the aperture stop S is provided on the image side surface of the optical path conversion element P.
  • the rear lens group GR includes a biconvex positive lens L2, a biconvex positive lens L3, and a negative meniscus lens L4 having a convex surface facing the image side.
  • the biconvex positive lens L3 and the negative meniscus lens L4 form a cemented lens having a positive refractive power. Both surfaces of the biconvex positive lens L2 are equal R surfaces.
  • a filter F2, a glass lid GL, and a cover glass CG are disposed in the rear lens group GR. The filter F2 is disposed between the biconvex positive lens L2 and the cemented lens.
  • FIG. 14 is a diagram showing a cross-sectional configuration of the perspective objective optical system according to Example 8 and aberration diagrams, where (a) is a lens cross section, (b) is spherical aberration (SA), and (c) is astigmatism. (AS) and (d) show distortion aberration (DT), and (e) shows lateral chromatic aberration (CC).
  • SA spherical aberration
  • DT distortion aberration
  • CC lateral chromatic aberration
  • the perspective objective optical system according to the eighth embodiment includes, in order from the object side, a front lens group GF having a negative refractive power, an optical path conversion element P, an aperture stop S, and a positive refractive power.
  • Rear lens group GR Rear lens group
  • the front lens group GF includes a plano-concave negative lens L1 having a flat object side. Sapphire is used for the planoconcave negative lens L1.
  • a filter F1 is disposed in the front lens group GF. The filter F1 is disposed between the plano-concave negative lens L1 and the optical path conversion element P.
  • the optical path conversion element P is disposed between the front lens group GF and the rear lens group GR.
  • the optical path conversion element P is a prism.
  • a high refractive index glass material having a refractive index of 1.8 or more is used for the prism.
  • the brightness stop S is disposed between the optical path conversion element P and the rear lens group GR. More specifically, the aperture stop S is provided on the image side surface of the optical path conversion element P.
  • the rear lens group GR includes a biconvex positive lens L2, a biconvex positive lens L3, and a negative meniscus lens L4 having a convex surface facing the image side.
  • the biconvex positive lens L3 and the negative meniscus lens L4 form a cemented lens having a positive refractive power.
  • the absolute value of the radius of curvature of the object side surface of the biconvex positive lens L2 is larger than the absolute value of the radius of curvature of the image side surface.
  • a filter F2, a glass lid GL, and a cover glass CG are disposed in the rear lens group GR.
  • the filter F2 is disposed between the biconvex positive lens L2 and the cemented lens.
  • FIG. 15 is a diagram illustrating a cross-sectional configuration of a perspective objective optical system according to Example 9, and aberration diagrams.
  • FIG. 15A is a lens cross section
  • FIG. 15B is spherical aberration (SA)
  • FIG. (AS) and (d) show distortion aberration (DT)
  • CC lateral chromatic aberration
  • the perspective objective optical system according to the ninth embodiment has a negative refractive power front lens group GF, an optical path conversion element P, an aperture stop S, and a positive refractive power in order from the object side.
  • Rear lens group GR Rear lens group
  • the front lens group GF includes a plano-concave negative lens L1 having a flat object side.
  • a filter F1 is disposed in the front lens group GF.
  • the filter F1 is disposed between the plano-concave negative lens L1 and the optical path conversion element P.
  • the optical path conversion element P is disposed between the front lens group GF and the rear lens group GR.
  • the optical path conversion element P is a prism.
  • a high refractive index glass material having a refractive index of 1.8 or more is used for the prism.
  • the brightness stop S is disposed between the optical path conversion element P and the rear lens group GR. More specifically, the aperture stop S is provided on the image side surface of the optical path conversion element P.
  • the rear lens group GR includes a biconvex positive lens L2, a biconvex positive lens L3, and a negative meniscus lens L4 having a convex surface facing the image side.
  • the biconvex positive lens L3 and the negative meniscus lens L4 form a cemented lens having a positive refractive power. Both surfaces of the biconvex positive lens L2 are equal R surfaces.
  • a glass lid GL and a cover glass CG are disposed in the rear lens group GR.
  • the function as an optical filter is concentrated in the filter F1. Therefore, only one optical filter is arranged in the perspective objective optical system.
  • FIG. 16 is a diagram showing a cross-sectional configuration of a perspective objective optical system according to Example 10 and aberration diagrams, where (a) is a lens cross section, (b) is spherical aberration (SA), and (c) is astigmatism. (AS) and (d) show distortion aberration (DT), and (e) shows lateral chromatic aberration (CC).
  • SA spherical aberration
  • DT distortion aberration
  • CC lateral chromatic aberration
  • the oblique objective optical system of Example 10 includes, in order from the object side, a front lens unit GF having a negative refractive power, an optical path conversion element P, an aperture stop S, and a positive refractive power.
  • Rear lens group GR Rear lens group
  • the front lens group GF includes a plano-concave negative lens L1 having a flat object side.
  • a filter F1 is disposed in the front lens group GF.
  • the filter F1 is disposed between the plano-concave negative lens L1 and the optical path conversion element P.
  • the optical path conversion element P is disposed between the front lens group GF and the rear lens group GR.
  • the optical path conversion element P is a prism.
  • a high refractive index glass material having a refractive index of 1.8 or more is used for the prism.
  • the brightness stop S is disposed between the optical path conversion element P and the rear lens group GR. More specifically, the aperture stop S is provided on the image side surface of the optical path conversion element P.
  • the rear lens group GR includes a biconvex positive lens L2, a biconvex positive lens L3, and a negative meniscus lens L4 having a convex surface facing the image side.
  • the biconvex positive lens L3 and the negative meniscus lens L4 form a cemented lens having a positive refractive power. Both surfaces of the biconvex positive lens L2 are equal R surfaces.
  • a filter F2, a glass lid GL, and a cover glass CG are disposed in the rear lens group GR. The filter F2 is disposed between the biconvex positive lens L2 and the cemented lens.
  • FIG. 17 is a diagram showing a cross-sectional configuration of a perspective objective optical system according to Example 11 and aberration diagrams, where (a) is a lens cross section, (b) is spherical aberration (SA), and (c) is astigmatism. (AS) and (d) show distortion aberration (DT), and (e) shows lateral chromatic aberration (CC).
  • SA spherical aberration
  • DT distortion aberration
  • CC lateral chromatic aberration
  • the oblique objective optical system of Example 11 has a negative refractive power front lens group GF, an optical path conversion element P, an aperture stop S, and a positive refractive power in order from the object side.
  • Rear lens group GR Rear lens group
  • the front lens group GF includes a plano-concave negative lens L1 having a flat object side.
  • a filter F1 is disposed in the front lens group GF.
  • the filter F1 is disposed between the plano-concave negative lens L1 and the optical path conversion element P.
  • the optical path conversion element P is disposed between the front lens group GF and the rear lens group GR.
  • the optical path conversion element P is a prism.
  • a high refractive index glass material having a refractive index of 1.8 or more is used for the prism.
  • the brightness stop S is disposed between the optical path conversion element P and the rear lens group GR. More specifically, the aperture stop S is provided on the image side surface of the optical path conversion element P.
  • the rear lens group GR includes a biconvex positive lens L2, a biconvex positive lens L3, and a negative meniscus lens L4 having a convex surface facing the image side.
  • the biconvex positive lens L3 and the negative meniscus lens L4 form a cemented lens having a positive refractive power.
  • the absolute value of the radius of curvature of the object side surface of the biconvex positive lens L2 is larger than the absolute value of the radius of curvature of the image side surface.
  • a filter F2, a glass lid GL, and a cover glass CG are disposed in the rear lens group GR.
  • the filter F2 is disposed between the biconvex positive lens L2 and the cemented lens.
  • FIG. 18 is a diagram showing a cross-sectional configuration of a perspective objective optical system according to Example 12 and aberration diagrams, where (a) is a lens cross section, (b) is spherical aberration (SA), and (c) is astigmatism. (AS) and (d) show distortion aberration (DT), and (e) shows lateral chromatic aberration (CC).
  • SA spherical aberration
  • DT distortion aberration
  • CC lateral chromatic aberration
  • the squint objective optical system of the twelfth embodiment has, in order from the object side, a front lens group GF having a negative refractive power, an optical path conversion element P, an aperture stop S, and a positive refractive power.
  • Rear lens group GR Rear lens group
  • the front lens group GF includes a plano-concave negative lens L1 having a flat object side.
  • a filter F1 is disposed in the front lens group GF.
  • the filter F1 is disposed between the plano-concave negative lens L1 and the optical path conversion element P.
  • the optical path conversion element P is disposed between the front lens group GF and the rear lens group GR.
  • the optical path conversion element P is a prism.
  • a high refractive index glass material having a refractive index of 1.8 or more is used for the prism.
  • the brightness stop S is disposed between the optical path conversion element P and the rear lens group GR. More specifically, the aperture stop S is provided on the image side surface of the optical path conversion element P.
  • the rear lens group GR includes a biconvex positive lens L2, a biconvex positive lens L3, and a negative meniscus lens L4 having a convex surface facing the image side.
  • the biconvex positive lens L3 and the negative meniscus lens L4 form a cemented lens having a positive refractive power.
  • the absolute value of the radius of curvature of the object side surface of the biconvex positive lens L2 is larger than the absolute value of the radius of curvature of the image side surface.
  • a filter F2, a glass lid GL, and a cover glass CG are disposed in the rear lens group GR.
  • the filter F2 is disposed between the biconvex positive lens L2 and the cemented lens.
  • FIG. 19 is a diagram illustrating a cross-sectional configuration of a perspective objective optical system according to Example 13 and aberration diagrams, where (a) is a lens cross section, (b) is spherical aberration (SA), and (c) is astigmatism. (AS) and (d) show distortion aberration (DT), and (e) shows lateral chromatic aberration (CC).
  • SA spherical aberration
  • DT distortion aberration
  • CC lateral chromatic aberration
  • the oblique objective optical system includes, in order from the object side, a front lens group GF having a negative refractive power, an optical path conversion element P, an aperture stop S, and a positive refractive power.
  • Rear lens group GR Rear lens group
  • the front lens group GF includes a plano-concave negative lens L1 having a flat object side.
  • a filter F1 is disposed in the front lens group GF.
  • the filter F1 is disposed between the plano-concave negative lens L1 and the optical path conversion element P.
  • the optical path conversion element P is disposed between the front lens group GF and the rear lens group GR.
  • the optical path conversion element P is a prism.
  • a high refractive index glass material having a refractive index of 1.8 or more is used for the prism.
  • the brightness stop S is disposed between the optical path conversion element P and the rear lens group GR. More specifically, the aperture stop S is provided on the image side surface of the optical path conversion element P.
  • the rear lens group GR includes a biconvex positive lens L2, a biconvex positive lens L3, and a negative meniscus lens L4 having a convex surface facing the image side.
  • the biconvex positive lens L3 and the negative meniscus lens L4 form a cemented lens having a positive refractive power.
  • the absolute value of the radius of curvature of the object side surface of the biconvex positive lens L2 is larger than the absolute value of the radius of curvature of the image side surface.
  • a filter F2, a glass lid GL, and a cover glass CG are disposed in the rear lens group GR.
  • the filter F2 is disposed between the biconvex positive lens L2 and the cemented lens.
  • FIG. 20 is a diagram illustrating a cross-sectional configuration of a perspective objective optical system according to Example 14 and aberration diagrams, where (a) is a lens cross section, (b) is spherical aberration (SA), and (c) is astigmatism. (AS) and (d) show distortion aberration (DT), and (e) shows lateral chromatic aberration (CC).
  • SA spherical aberration
  • DT distortion aberration
  • CC lateral chromatic aberration
  • the oblique objective optical system of the fourteenth embodiment has, in order from the object side, a front lens unit GF having a negative refractive power, an optical path conversion element P, an aperture stop S, and a positive refractive power.
  • Rear lens group GR Rear lens group
  • the front lens group GF includes a plano-concave negative lens L1 having a flat object side.
  • the filter F1 is disposed between the plano-concave negative lens L1 and the optical path conversion element P.
  • the optical path conversion element P is disposed between the front lens group GF and the rear lens group GR.
  • the optical path conversion element P is a prism.
  • a low refractive index glass material having a refractive index of about 1.5 is used for the prism.
  • the brightness stop S is disposed between the optical path conversion element P and the rear lens group GR. More specifically, the aperture stop S is provided on the image side surface of the optical path conversion element P.
  • the rear lens group GR includes a biconvex positive lens L2, a biconvex positive lens L3, and a planoconcave negative lens L4.
  • the biconvex positive lens L3 and the plano-concave negative lens L4 form a cemented lens having a positive refractive power.
  • the absolute value of the radius of curvature of the object side surface of the biconvex positive lens L2 is larger than the absolute value of the radius of curvature of the image side surface.
  • a filter F2, a glass lid GL, and a cover glass CG are disposed in the rear lens group GR.
  • the filter F2 is disposed between the biconvex positive lens L2 and the cemented lens.
  • a low refractive index glass material is used for the prism. Therefore, it is necessary to increase the distance (air conversion length) between the front lens group GF and the rear lens group GR so that the prism can be arranged.
  • the low refractive index glass material has lower dispersion than the high refractive index glass material. Therefore, it is possible to correct chromatic aberration without using a high refractive index and abnormally dispersed glass material having an Abbe number of less than 20 for the cemented lens.
  • a glass material having a refractive index of about 1.8 and an Abbe number of about 22 is used for the plano-concave negative lens L4.
  • the distance between the front lens group and the rear lens group becomes longer than in the case of a high refractive index glass material, so the outer diameter of the negative lens increases. It becomes easy.
  • the lens diameter of the front lens group is the same as that of the other embodiments.
  • the refractive index difference between the biconvex positive lens L3 and the plano-concave negative lens L4 of the cemented lens is as small as about 0.07.
  • the image side surface of the plano-concave negative lens L4 is a flat surface. Therefore, the processability of the lens is good, and it is easy to determine before and after the lens at the time of assembly.
  • FIG. 21 is a diagram showing a cross-sectional configuration of the perspective objective optical system according to Example 15 and aberration diagrams, where (a) is a lens cross section, (b) is spherical aberration (SA), and (c) is astigmatism. (AS) and (d) show distortion aberration (DT), and (e) shows lateral chromatic aberration (CC).
  • SA spherical aberration
  • DT distortion aberration
  • CC lateral chromatic aberration
  • the perspective objective optical system of Example 15 is arranged in order from the object side, the front lens group GF having a negative refractive power, an optical path conversion element P, an aperture stop S, and a positive refractive power.
  • Rear lens group GR Rear lens group
  • the front lens group GF includes a plano-concave negative lens L1 having a flat object side.
  • a filter F1 is disposed in the front lens group GF.
  • the filter F1 is disposed between the plano-concave negative lens L1 and the optical path conversion element P.
  • the optical path conversion element P is disposed between the front lens group GF and the rear lens group GR.
  • the optical path conversion element P is a prism.
  • a high refractive index glass material having a refractive index of 1.8 or more is used for the prism.
  • the brightness stop S is disposed between the optical path conversion element P and the rear lens group GR. More specifically, the aperture stop S is provided on the image side surface of the optical path conversion element P.
  • the rear lens group GR includes a biconvex positive lens L2, a biconvex positive lens L3, and a negative meniscus lens L4 having a convex surface facing the image side.
  • the biconvex positive lens L3 and the negative meniscus lens L4 form a cemented lens having a positive refractive power.
  • the absolute value of the radius of curvature of the object side surface of the biconvex positive lens L2 is larger than the absolute value of the radius of curvature of the image side surface.
  • a filter F2, a glass lid GL, and a cover glass CG are disposed in the rear lens group GR.
  • the filter F2 is disposed between the biconvex positive lens L2 and the cemented lens.
  • the angle of view is widened to 120 degrees, but by using a high refractive index glass material having a refractive index of 1.8 or more for the prism, the plano-concave negative lens L1
  • the curvature radius (absolute value) of the image side surface is not reduced.
  • it is a bright and high-performance perspective objective optical system with an F number of about 3.6.
  • the perspective objective optical system of each embodiment includes the front lens group disposed on the object side of the prism, the rear lens group disposed on the image side of the prism, and the front lens group having negative refraction.
  • the rear lens group has a positive refractive power and is composed of a positive refractive power lens and a cemented lens having a positive refractive power. In which a lens having a positive refractive power and a lens having a negative refractive power are sequentially joined, and an aperture stop is provided between the prism and the rear lens group.
  • the perspective objective optical system of each embodiment has an optimal lens configuration that improves optical performance in response to the downsizing of the image sensor and the increase in the number of pixels, and this configuration reduces the diameter of the distal end portion of the endoscope. Can also contribute. Furthermore, since the perspective objective optical system of each example satisfies each conditional expression, various aberrations are corrected well.
  • r is the radius of curvature of each surface
  • d is the thickness or air spacing of each optical member
  • nd is the refractive index of each optical member with respect to the d-line
  • ⁇ d is the Abbe number of each optical member with respect to the d-line
  • f is a perspective view
  • IH is the image height
  • ⁇ is the half field angle
  • f F is the focal length of the front lens group
  • f R is the focal length of the rear lens group
  • D1 is the negative lens of the front lens group.
  • the air-equivalent length from the image side surface of the last lens of D2 is the rear lens group to the image plane
  • R c is a curvature of the cemented surface of the cemented lens in the rear lens group
  • F 2 represents the focal length of the positive lens in the rear lens group
  • f 3 represents the focal length of the cemented lens in the rear lens group
  • TW represents the light incident angle on the image plane at the maximum image height.
  • the unit of r, d, IH, air conversion length and focal length is mm.
  • F is standardized to 1 mm.
  • Example 1 Example 2
  • Example 3 Example 4
  • Example 5 (1) f F / f -1.553 -1.528 -1.468 -1.675 -1.675 (2) f R / f 2.062 2.056 2.069 2.108 2.108 (3)
  • Example 6 Example 7
  • Example 8 Example 9
  • Example 10 Example 10
  • FIG. 22 is a configuration example of an endoscope apparatus using the perspective objective optical system of the present embodiment.
  • the endoscope apparatus 20 includes a perspective endoscope 21 (hereinafter referred to as “endoscope 21”), a video processor 22, and a monitor 23.
  • the endoscope 21 includes an insertion portion 21a and a signal cable 21b.
  • a perspective objective optical system 24 is disposed at the distal end of the insertion portion 21a.
  • the perspective objective optical system 24 is a perspective objective optical system for front-view observation.
  • any one of the perspective objective optical systems of Examples 1 to 15 is used.
  • an illumination optical system for illuminating the subject 25 is arranged in the vicinity of the oblique objective optical system 24.
  • the illumination optical system includes a light source, an illumination optical element, and an optical fiber bundle.
  • the light source include a light emitting diode (LED: Light Emitting Diode) and a laser diode (LD: Laser Diode).
  • An example of the illumination optical element is a lens element.
  • the lens element has a function of diffusing or condensing illumination light.
  • the optical fiber bundle transmits illumination light to the endoscope 21.
  • the endoscope 21 is connected to the video processor 22 via the signal cable 21b.
  • An image of the subject 25 imaged by the squint objective optical system 24 is captured by an image sensor.
  • the captured image of the subject 25 is converted into a video signal by an electric circuit system built in the video processor 22.
  • a subject image 26 is displayed on the monitor 23 based on the video signal.
  • an electric circuit system for driving a light source such as an LED is provided.
  • a light emitting element such as an LED or LD in the endoscope 21
  • providing these light emitting elements at the distal end portion of the endoscope 21 eliminates the need to provide an optical fiber bundle for transmitting illumination light.
  • a xenon lamp or a halogen lamp may be used as the light source.
  • a light source device incorporating a light source is integrated with the video processor 22.
  • the light source device may be configured separately from the video processor 22. In this case, the light source device and the video processor 22 are connected to the endoscope 21, respectively.
  • the perspective objective optical system of the present invention it is most suitable for an image pickup device having a large number of pixels and a small size while improving assemblability and attachment to an endoscope tip.
  • a high-performance and compact perspective objective optical system can be provided.
  • a high-quality image can be obtained, and a perspective endoscope having a thinned tip can be provided.
  • the invention of the following structures is guide
  • the front lens group including a negative lens, an optical path conversion element, an aperture stop, and a rear lens group having a positive refractive power
  • the rear lens group includes a positive lens and a cemented lens having a positive refractive power.
  • the cemented lens is composed of a positive lens and a negative lens in order from the object side.
  • the present invention can be easily assembled and attached to the distal end portion of the endoscope with high accuracy and is useful for a high-performance and compact perspective objective optical system. Moreover, it is useful for a perspective endoscope having a high-quality image and having a thinned tip.

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Abstract

An oblique-view objective optical system is constituted by a front lens group GF composed of a negative lens, an optical path conversion element P, a stop S, and a rear lens group GR with a positive refractive power in order from an object side. The rear lens group GR is composed of a positive lens L2 and a cemented lens with a positive refractive power. The cemented lens is constituted by a positive lens L3 and a negative lens L4 in order from the object side. The oblique-view objective optical system satisfies the following conditional expressions (1), (2), and (3): −2.0 < fF / f < −1.3 (1) 1.7 < fR / f <2.7 (2) 0.63 < | fF / fR | < 0.88 (3) Where fF represents the focal distance of the front lens group; fR represents the focal distance of the rear lens group; and f represents the focal distance of the whole oblique-view objective optical system.

Description

斜視対物光学系及びそれを備えた斜視用内視鏡Obstacle objective optical system and endoscope for squint having the same
　本発明は、光路変換素子を具備した斜視対物光学系及びそれを備えた斜視用内視鏡に関するものである。 The present invention relates to a perspective objective optical system including an optical path conversion element and a perspective endoscope including the same.
　近年、ＣＣＤ（Charge　Coupled　Devices）やＣ－ＭＯＳ（Complementary　Metal　Oxide　Semiconductor）等の撮像素子では、微細化技術の進歩によって、画素の微細化と素子自体の小型化が進んでいる。特に最近では、非常に微細な画素を持つ撮像素子、例えば、画素ピッチが約２～３μｍという撮像素子が製造されてきている。このように、近年の撮像素子は、以前に比べて多画素で小型になってきている。 In recent years, in image sensors such as CCD (Charge Coupled Devices) and C-MOS (Complementary Metal Oxide Semiconductor), pixel miniaturization and element miniaturization are progressing due to progress in miniaturization technology. Particularly recently, an image sensor having very fine pixels, for example, an image sensor having a pixel pitch of about 2 to 3 μm has been manufactured. As described above, recent image pickup devices have become smaller and have a larger number of pixels than before.
　また、光学系のレンズ外径や全長を小型化すると、光学系から出射する光線を、撮像素子の受光面に対して垂直に入射させることが困難になる。この場合、光線は受光面に対して斜めに入射する（以下、「斜入射」という）。そのため、近年のＣＣＤやＣ－ＭＯＳ等の撮像素子は、受光面への最適な光線の入射が斜入射であることを前提として設計されている。このように、近年の撮像素子は斜入射特性を有している。 In addition, when the lens outer diameter and the overall length of the optical system are reduced, it becomes difficult to make the light emitted from the optical system incident perpendicularly to the light receiving surface of the image sensor. In this case, the light ray is incident obliquely on the light receiving surface (hereinafter referred to as “oblique incidence”). For this reason, recent imaging devices such as CCDs and C-MOSs are designed on the assumption that the optimum light beam incident on the light receiving surface is oblique incidence. Thus, recent image sensors have oblique incidence characteristics.
　多画素で小型な撮像素子を内視鏡に用いることで、画像の高画質化と内視鏡の細径化が可能になる。それに伴って、内視鏡用の対物光学系には、高性能で小型の対物光学系が求められることになる。高性能な光学系とは、例えば、分解能が高く、収差が良好に補正されている光学系である。 ¡By using a multi-pixel, small image sensor for the endoscope, it is possible to improve the image quality and reduce the diameter of the endoscope. Accordingly, a high-performance and compact objective optical system is required for an endoscope objective optical system. A high-performance optical system is, for example, an optical system with high resolution and good aberration correction.
　内視鏡用の対物光学系の一つに、斜視対物光学系がある。斜視対物光学系では、前方視、側方視又は後方視が行われる。 There is a perspective objective optical system as one of the objective optical systems for endoscopes. In the perspective objective optical system, forward view, side view, or backward view is performed.
　図１は、従来の斜視対物光学系の例である。斜視対物光学系１は、側方視を行う斜視対物光学系である。斜視対物光学系１は、前側レンズ群２、プリズム３及び後側レンズ群４で構成されている。斜視対物光学系１では、プリズム３によって、前側レンズ群２の光軸と後側レンズ群４の光軸とが直交した状態になっている。 FIG. 1 is an example of a conventional perspective objective optical system. The perspective objective optical system 1 is a perspective objective optical system that performs a side view. The oblique objective optical system 1 includes a front lens group 2, a prism 3 and a rear lens group 4. In the oblique objective optical system 1, the optical axis of the front lens group 2 and the optical axis of the rear lens group 4 are orthogonal to each other by the prism 3.
　図２は、従来の斜視対物光学系の別の例である。斜視対物光学系５は、前方視を行う斜視対物光学系である。斜視対物光学系５は、前側レンズ群６、プリズム７及び後側レンズ群８で構成されている。斜視対物光学系５では、プリズム７によって、前側レンズ群６の光軸と後側レンズ群８の光軸とが交差した状態（ただし、直交状態ではない）になっている。 FIG. 2 is another example of a conventional perspective objective optical system. The perspective objective optical system 5 is a perspective objective optical system that performs forward viewing. The oblique objective optical system 5 includes a front lens group 6, a prism 7 and a rear lens group 8. In the oblique objective optical system 5, the prism 7 causes the optical axis of the front lens group 6 and the optical axis of the rear lens group 8 to intersect (but not in an orthogonal state).
　図１や図２に示すように、斜視対物光学系では、大きな硝路長の光路変換素子が光学系中に配置される。そのため、特に斜視対物光学系では、光路変換素子、例えばプリズムを配置するための大きなスペースが必要となる。その結果、斜視対物光学系では、直視の対物光学系に比べて光学系の全長が長くなる。このように、斜視対物光学系は、直視の対物光学系に比べて大型になる傾向があるため、斜視対物光学系には一層の小型化が要求される。特許文献１～５には、斜視対物光学系が開示されている。 As shown in FIGS. 1 and 2, in the perspective objective optical system, an optical path conversion element having a large glass path length is arranged in the optical system. For this reason, particularly in a perspective objective optical system, a large space for arranging an optical path conversion element such as a prism is required. As a result, in the perspective objective optical system, the total length of the optical system is longer than that of the direct-view objective optical system. Thus, since the perspective objective optical system tends to be larger than the direct-view objective optical system, the perspective objective optical system is required to be further downsized. Patent Documents 1 to 5 disclose perspective objective optical systems.
　特許文献１に開示された斜視対物光学系は、前群発散レンズ系と、後群収斂レンズ系と、で構成されている。この斜視対物光学系は、イメージファイバに用いられることを前提とした光学系である。そのため、この斜視対物光学系では、斜視対物光学系から出射する光線を、ファイバの入射端面に対してほぼ垂直に入射できるようにしている。 The perspective objective optical system disclosed in Patent Document 1 includes a front group diverging lens system and a rear group converging lens system. This perspective objective optical system is an optical system premised on being used for an image fiber. For this reason, in this oblique objective optical system, the light beam emitted from the oblique objective optical system can be incident substantially perpendicular to the incident end face of the fiber.
　特許文献２に開示された斜視対物光学系は、１枚の負レンズからなる第１レンズ群と、正の屈折力を有する第２レンズ群と、で構成されている。この斜視対物光学系では、色収差補正のために、第１レンズ群の負レンズとプリズムに、分散が小さい硝材（アッベ数が大きい硝材）が用いられている。 The perspective objective optical system disclosed in Patent Document 2 includes a first lens group including one negative lens and a second lens group having a positive refractive power. In this perspective objective optical system, a glass material having a small dispersion (a glass material having a large Abbe number) is used for the negative lens and the prism of the first lens group in order to correct chromatic aberration.
　特許文献３に開示された斜視対物光学系は、負の焦点距離を有する前群と、正の焦点距離を有する後群と、で構成されている。 The perspective objective optical system disclosed in Patent Document 3 is composed of a front group having a negative focal length and a rear group having a positive focal length.
　特許文献４に開示された斜視対物光学系は、負の屈折力の単レンズからなる第１レンズ群と、正の屈折力を有する第２レンズ群と、正の屈折力を有する第３レンズ群と、で構成されている。この斜視対物光学系では、第３レンズ群を、物体側から順に、負レンズと正レンズからなる接合レンズで構成している。このようにすることで、テレセントリック性を確保している。すなわち、特許文献４に開示された斜視対物光学系では、斜視対物光学系から出射する光線を、ＣＣＤの受光面に対してほぼ垂直に入射できるようにしている。 The perspective objective optical system disclosed in Patent Document 4 includes a first lens group composed of a single lens having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power. And is composed of. In this perspective objective optical system, the third lens group is composed of a cemented lens composed of a negative lens and a positive lens in order from the object side. In this way, telecentricity is ensured. That is, in the perspective objective optical system disclosed in Patent Document 4, a light beam emitted from the perspective objective optical system can be incident substantially perpendicularly to the light receiving surface of the CCD.
　特許文献５に開示された斜視対物光学系は、負の第１群と、正の第２群と、から構成されている。 The perspective objective optical system disclosed in Patent Document 5 includes a negative first group and a positive second group.
　ところで、斜視対物光学系や直視の対物光学系では、光学系は枠部材によって保持されている。光学系は、組立時に、枠部材を介して組立用の治工具に取り付けられる。また、組立てられた後の光学系は、枠部材を介して内視鏡先端部へ組込まれる。そのため、枠部材の嵌合部については、ある程度の長さを確保する必要がある。 By the way, in a perspective objective optical system or a direct-view objective optical system, the optical system is held by a frame member. The optical system is attached to a jig for assembly through a frame member at the time of assembly. Further, the assembled optical system is assembled into the endoscope distal end portion via the frame member. Therefore, it is necessary to secure a certain length for the fitting portion of the frame member.
　図３は、斜視対物光学系の枠部材の例である。斜視対物光学系９は、側方視を行う斜視対物光学系である。斜視対物光学系９は、前側レンズ群１０、プリズム１１及び後側レンズ群１２で構成されている。斜視対物光学系９では、プリズム１１における１回の反射によって、前側レンズ群１０の光軸と後側レンズ群１２の光軸とが直交した状態になっている。 FIG. 3 is an example of a frame member of the perspective objective optical system. The perspective objective optical system 9 is a perspective objective optical system that performs a side view. The oblique objective optical system 9 includes a front lens group 10, a prism 11, and a rear lens group 12. In the perspective objective optical system 9, the optical axis of the front lens group 10 and the optical axis of the rear lens group 12 are orthogonal to each other by one reflection at the prism 11.
　斜視対物光学系９では、前側レンズ群１０とプリズム１１が枠部材１３で保持され、後側レンズ群１２が枠部材１４で保持されている。また、撮像素子１５が枠部材１６で保持されている。 In the perspective objective optical system 9, the front lens group 10 and the prism 11 are held by the frame member 13, and the rear lens group 12 is held by the frame member 14. Further, the image sensor 15 is held by the frame member 16.
　図４と図５は、斜視対物光学系の枠部材の別の例である。斜視対物光学系１７や斜視対物光学系１８は、前方視を行う斜視対物光学系である。斜視対物光学系１７や斜視対物光学系１８では、プリズムにおける２回の反射によって、前側レンズ群の光軸と後側レンズ群の光軸とが交差した状態になっている。斜視対物光学系１７では２つの枠部材が用いられ、斜視対物光学系１８では３つの枠部材が用いられている。 4 and 5 show another example of the frame member of the perspective objective optical system. The oblique objective optical system 17 and the oblique objective optical system 18 are oblique objective optical systems that perform forward viewing. In the oblique objective optical system 17 and the oblique objective optical system 18, the optical axis of the front lens group and the optical axis of the rear lens group intersect with each other by two reflections on the prism. The perspective objective optical system 17 uses two frame members, and the perspective objective optical system 18 uses three frame members.
特開昭５１－６２０５３号公報JP 51-62053 A 特許３３８５０９０号公報Japanese Patent No. 3385090 特許３５７４４８４号公報Japanese Patent No. 3574484 特許４４３９１８４号公報Japanese Patent No. 4439184 特許４８１４７４６号公報Japanese Patent No. 4814746
　特許文献１に開示された斜視対物光学系は光学系全体が大きく、また、光学性能も不十分である。そのため、特許文献１に開示された斜視対物光学系を、多画素で小型なＣＣＤ等の撮像素子への適用が可能な斜視対物光学系、すなわち、高性能化と小型化に対応した斜視対物光学系に適用することはできない。 The perspective objective optical system disclosed in Patent Document 1 has a large optical system as a whole and has insufficient optical performance. Therefore, the perspective objective optical system disclosed in Patent Document 1 can be applied to an imaging device such as a CCD having a small number of pixels, that is, a perspective objective optical system corresponding to high performance and downsizing. It cannot be applied to the system.
　また、特許文献２に開示された斜視対物光学系では、色収差補正のために、第１レンズ群の負レンズとプリズムの各々に、低屈折率の硝材が用いられている。この場合、特に、明るさ絞りよりも物体側の空気換算長が長くなる。その結果、負レンズの外径やプリズムの外径が大きくなってしまう。そのため、特許文献２に開示された斜視対物光学系を、高性能化と小型化に対応した斜視対物光学系へ適用することはできない。 In the perspective objective optical system disclosed in Patent Document 2, a glass material having a low refractive index is used for each of the negative lens and the prism of the first lens group in order to correct chromatic aberration. In this case, the air equivalent length on the object side is particularly longer than the aperture stop. As a result, the outer diameter of the negative lens and the outer diameter of the prism are increased. Therefore, the perspective objective optical system disclosed in Patent Document 2 cannot be applied to a perspective objective optical system corresponding to high performance and downsizing.
　また、特許文献３に開示された斜視対物光学系では、バックフォーカスが長いため光学系全体が大型化してしまう。また、前群における負レンズの焦点距離が短いので、前群の負の屈折力が大きい。しかしながら、バックフォーカスが長いため、接合レンズの焦点距離が長くなっている。このように、光学系全体での屈折力のバランスが悪いため、光学性能が十分ではない。そのため、特許文献３に開示された斜視対物光学系を、高性能化と小型化に対応した斜視対物光学系へ適用することはできない。 Further, in the perspective objective optical system disclosed in Patent Document 3, since the back focus is long, the entire optical system becomes large. Further, since the focal length of the negative lens in the front group is short, the negative refractive power of the front group is large. However, since the back focus is long, the focal length of the cemented lens is long. Thus, the optical performance is not sufficient because the balance of refractive power in the entire optical system is poor. Therefore, the perspective objective optical system disclosed in Patent Document 3 cannot be applied to a perspective objective optical system corresponding to high performance and downsizing.
　また、特許文献４に開示された斜視対物光学系では、テレセントリック性が確保されている。しかしながら、近年の撮像素子は斜入射特性を有しているので、光学系においてテレセントリック性が確保されている必要が無い。特許文献４に開示された斜視対物光学系では、斜視対物光学系から出射する光線の角度は、撮像素子の斜入射特性を満足する角度からむしろ乖離してしまう。その結果、画像の周辺部に、明るさのムラや色のムラが生じてしまう。そのため、特許文献４に開示された斜視対物光学系を、高性能化と小型化に対応した斜視対物光学系へ適用することはできない。 In the perspective objective optical system disclosed in Patent Document 4, telecentricity is ensured. However, since recent image sensors have oblique incidence characteristics, it is not necessary to ensure telecentricity in the optical system. In the oblique objective optical system disclosed in Patent Document 4, the angle of the light beam emitted from the oblique objective optical system is rather deviated from the angle satisfying the oblique incidence characteristic of the image sensor. As a result, brightness unevenness and color unevenness occur in the peripheral portion of the image. Therefore, the perspective objective optical system disclosed in Patent Document 4 cannot be applied to a perspective objective optical system corresponding to high performance and downsizing.
　また、特許文献５に開示された斜視対物光学系では、画角が大きいため、第１群の焦点距離が短くなっている（第１群の負屈折力が大きくなっている）。一方、フィルタ類を配置するためには、光学系の全長とバックフォーカスを長くする必要があることから、第２群の焦点距離が長くなっている（第２群の正屈折力が小さくなっている）。これだと、負屈折力と正屈折力のバランスが崩れてしまうので、像面湾曲及び非点収差が発生してしまう。さらに、特許文献５に開示された斜視対物光学系では、像高が高いので、第２群のレンズ外径も大きくなっている。そのため、特許文献５に開示された斜視対物光学系を、高性能化と小型化に対応した斜視対物光学系へ適用することはできない。 Further, in the perspective objective optical system disclosed in Patent Document 5, since the angle of view is large, the focal length of the first group is short (the negative refractive power of the first group is large). On the other hand, in order to arrange the filters, it is necessary to lengthen the overall length of the optical system and the back focus, so that the focal length of the second group is long (the positive refractive power of the second group is small). ) In this case, since the balance between the negative refractive power and the positive refractive power is lost, field curvature and astigmatism occur. Furthermore, in the perspective objective optical system disclosed in Patent Document 5, since the image height is high, the outer diameter of the lens of the second group is also large. Therefore, the perspective objective optical system disclosed in Patent Document 5 cannot be applied to a perspective objective optical system corresponding to high performance and downsizing.
　以上のように、特許文献１～５に開示された斜視対物光学系では、高性能化と小型化に対応した斜視対物光学系を実現することは難しい。 As described above, with the perspective objective optical systems disclosed in Patent Documents 1 to 5, it is difficult to realize a perspective objective optical system corresponding to high performance and downsizing.
　また、図３に示すように、枠部材１３と枠部材１４は、嵌合部１３ａと嵌合部１４ａとで接続されている。斜視対物光学系９の組立時、枠部材１３と枠部材１４は、各々治工具によって保持される。そして、両者の相対位置が調整された後、固定される。 Moreover, as shown in FIG. 3, the frame member 13 and the frame member 14 are connected by the fitting part 13a and the fitting part 14a. When the oblique objective optical system 9 is assembled, the frame member 13 and the frame member 14 are each held by a jig. And after fixing the relative position of both, it fixes.
　ここで、斜視対物光学系９が小型になると、枠部材１３と枠部材１４も短くなる。枠部材１３と枠部材１４が短くなり過ぎると、枠部材１３を保持する治工具と枠部材１４を保持する治工具とが干渉してしまう。そのため、斜視対物光学系９の組立てができなくなる。 Here, when the perspective objective optical system 9 is reduced in size, the frame member 13 and the frame member 14 are also shortened. If the frame member 13 and the frame member 14 become too short, the jig holding the frame member 13 and the jig holding the frame member 14 interfere with each other. Therefore, it becomes impossible to assemble the perspective objective optical system 9.
　また、斜視対物光学系９が小型になると、嵌合部１３ａの長さと嵌合部１４ａの長さを、各々十分に確保することが困難になる。この場合、枠部材１３と枠部材１４を、予め決められた状態に保つことが困難になる。そのため、斜視対物光学系９を精度良く組立てることができない。 Further, when the squint objective optical system 9 is downsized, it becomes difficult to sufficiently secure the length of the fitting portion 13a and the length of the fitting portion 14a. In this case, it becomes difficult to keep the frame member 13 and the frame member 14 in a predetermined state. Therefore, the perspective objective optical system 9 cannot be assembled with high accuracy.
　枠部材１４と枠部材１６は、嵌合部１４ｂと嵌合部１６ａとで接続されている。斜視対物光学系９が小型になると、枠部材１４と枠部材１６についても上述の問題が生じる。 The frame member 14 and the frame member 16 are connected by the fitting part 14b and the fitting part 16a. When the perspective objective optical system 9 is reduced in size, the above-described problem also occurs with respect to the frame member 14 and the frame member 16.
　また、斜視対物光学系９は、枠部材１３の嵌合部１３ｂを介して内視鏡先端部へ組込まれる。斜視対物光学系９が小型になると、嵌合部１３ｂの長さを十分に確保することが困難になる。この場合、内視鏡先端部に対して、枠部材１３を予め決められた状態に保つことが困難になる。そのため、斜視対物光学系９を内視鏡先端部に精度良く取り付けることができない。 Further, the perspective objective optical system 9 is incorporated into the endoscope distal end portion through the fitting portion 13 b of the frame member 13. If the perspective objective optical system 9 is downsized, it is difficult to ensure a sufficient length of the fitting portion 13b. In this case, it becomes difficult to keep the frame member 13 in a predetermined state with respect to the distal end portion of the endoscope. Therefore, the perspective objective optical system 9 cannot be attached to the endoscope distal end with high accuracy.
　また、図４と図５に示すように、斜視対物光学系１７では２つの枠部材が用いられ、斜視対物光学系１８では３つの枠部材が用いられている。よって、これらの斜視対物光学系においても、上述の問題が生じる。 Also, as shown in FIGS. 4 and 5, the perspective objective optical system 17 uses two frame members, and the perspective objective optical system 18 uses three frame members. Therefore, the above-described problems occur in these perspective objective optical systems.
　本発明は、このような問題点に鑑みてなされたものであり、組立てや内視鏡先端部への取り付けを高精度且つ容易に行えると共に、高性能で小型な斜視対物光学系を提供することを目的とする。また、高画質の画像が得られると共に、細径化された先端部を有する斜視用内視鏡を提供する。 The present invention has been made in view of such problems, and provides a high-performance and compact perspective objective optical system that can be assembled and attached to an endoscope distal end with high accuracy and ease. With the goal. In addition, the present invention provides a perspective endoscope having a high-quality image and having a thinned tip.
　上述した課題を解決し、目的を達成するために、本発明の斜視対物光学系は、
　物体側から順に、負レンズからなる前側レンズ群と、光路変換素子と、明るさ絞りと、正の屈折力を有する後側レンズ群と、から構成され、
　後側レンズ群は、正レンズと、正の屈折力を有する接合レンズと、からなり、
　接合レンズは、物体側から順に、正レンズと負レンズとで構成され、
　以下の条件式（１）、（２）、（３）を満足する。
　－２．０＜ｆF／ｆ＜－１．３　　　（１）
　１．７＜ｆR／ｆ＜２．７　　　（２）
　０．６３＜｜ｆF／ｆR｜＜０．８８　　　（３）
　ただし、
　ｆFは、前側レンズ群の焦点距離、
　ｆRは、後側レンズ群の焦点距離、
　ｆは、斜視対物光学系全系の焦点距離、
である。 In order to solve the above-described problems and achieve the object, the perspective objective optical system of the present invention includes:
In order from the object side, the front lens group including a negative lens, an optical path conversion element, an aperture stop, and a rear lens group having a positive refractive power,
The rear lens group includes a positive lens and a cemented lens having a positive refractive power.
The cemented lens is composed of a positive lens and a negative lens in order from the object side.
The following conditional expressions (1), (2), and (3) are satisfied.
-2.0 <f F /f<-1.3 (1)
1.7 <f R /f<2.7 (2)
0.63 <| f F / f R | <0.88 (3)
However,
f F is the focal length of the front lens group,
f R is the focal length of the rear lens group,
f is the focal length of the entire oblique objective optical system,
It is.
　また、本発明の斜視用内視鏡は、
　上記の斜視対物光学系を備えることを特徴とする。 The perspective endoscope of the present invention is
The above-mentioned perspective objective optical system is provided.
　本発明によれば、組立てや内視鏡先端部への取り付けを高精度且つ容易に行えると共に、高性能で小型な斜視対物光学系を実現することができる。また、高画質の画像が得られると共に、細径化された先端部を有する斜視用内視鏡を提供することができる。 According to the present invention, assembly and attachment to the distal end portion of the endoscope can be easily performed with high accuracy, and a high-performance and compact perspective optical system can be realized. In addition, it is possible to provide a perspective endoscope having a high-quality image and having a thinned tip.
従来の斜視対物光学系を示す図である。It is a figure which shows the conventional perspective objective optical system. 従来の別の斜視対物光学系を示す図である。It is a figure which shows another conventional perspective objective optical system. 斜視対物光学系の枠部材を示す図である。It is a figure which shows the frame member of a perspective objective optical system. 斜視対物光学系の別の枠部材を示す図である。It is a figure which shows another frame member of a perspective objective optical system. 斜視対物光学系の別の枠部材を示す図である。It is a figure which shows another frame member of a perspective objective optical system. 本実施例に係る斜視対物光学系の断面構成を示す図と、プリズムを示す図である。It is a figure which shows the cross-sectional structure of the perspective objective optical system which concerns on a present Example, and a figure which shows a prism. 実施例１に係る斜視対物光学系の断面構成を示す図と、球面収差（ＳＡ）、非点収差（ＡＳ）、歪曲収差（ＤＴ）及び倍率色収差（ＣＣ）をそれぞれ示す収差図である。FIG. 6 is a diagram illustrating a cross-sectional configuration of a perspective objective optical system according to Example 1, and an aberration diagram illustrating spherical aberration (SA), astigmatism (AS), distortion (DT), and lateral chromatic aberration (CC). 実施例２に係る斜視対物光学系の断面構成を示す図と、球面収差（ＳＡ）、非点収差（ＡＳ）、歪曲収差（ＤＴ）及び倍率色収差（ＣＣ）をそれぞれ示す収差図である。FIG. 6 is a diagram illustrating a cross-sectional configuration of a perspective objective optical system according to Example 2, and aberration diagrams illustrating spherical aberration (SA), astigmatism (AS), distortion (DT), and lateral chromatic aberration (CC). 実施例３に係る斜視対物光学系の断面構成を示す図と、球面収差（ＳＡ）、非点収差（ＡＳ）、歪曲収差（ＤＴ）及び倍率色収差（ＣＣ）をそれぞれ示す収差図である。FIG. 6 is a diagram illustrating a cross-sectional configuration of a perspective objective optical system according to Example 3, and aberration diagrams illustrating spherical aberration (SA), astigmatism (AS), distortion (DT), and lateral chromatic aberration (CC). 実施例４に係る斜視対物光学系の断面構成を示す図と、球面収差（ＳＡ）、非点収差（ＡＳ）、歪曲収差（ＤＴ）及び倍率色収差（ＣＣ）をそれぞれ示す収差図である。FIG. 6 is a diagram illustrating a cross-sectional configuration of a perspective objective optical system according to Example 4 and aberration diagrams illustrating spherical aberration (SA), astigmatism (AS), distortion (DT), and lateral chromatic aberration (CC). 実施例５に係る斜視対物光学系の断面構成を示す図と、球面収差（ＳＡ）、非点収差（ＡＳ）、歪曲収差（ＤＴ）及び倍率色収差（ＣＣ）をそれぞれ示す収差図である。FIG. 10 is a diagram illustrating a cross-sectional configuration of a perspective objective optical system according to Example 5, and aberration diagrams illustrating spherical aberration (SA), astigmatism (AS), distortion (DT), and lateral chromatic aberration (CC). 実施例６に係る斜視対物光学系の断面構成を示す図と、球面収差（ＳＡ）、非点収差（ＡＳ）、歪曲収差（ＤＴ）及び倍率色収差（ＣＣ）をそれぞれ示す収差図である。FIG. 10 is a diagram illustrating a cross-sectional configuration of a perspective objective optical system according to Example 6, and aberration diagrams illustrating spherical aberration (SA), astigmatism (AS), distortion (DT), and lateral chromatic aberration (CC). 実施例７に係る斜視対物光学系の断面構成を示す図と、球面収差（ＳＡ）、非点収差（ＡＳ）、歪曲収差（ＤＴ）及び倍率色収差（ＣＣ）をそれぞれ示す収差図である。FIG. 10 is a diagram illustrating a cross-sectional configuration of a perspective objective optical system according to Example 7, and aberration diagrams illustrating spherical aberration (SA), astigmatism (AS), distortion (DT), and lateral chromatic aberration (CC). 実施例８に係る斜視対物光学系の断面構成を示す図と、球面収差（ＳＡ）、非点収差（ＡＳ）、歪曲収差（ＤＴ）及び倍率色収差（ＣＣ）をそれぞれ示す収差図である。FIG. 10 is a diagram illustrating a cross-sectional configuration of a perspective objective optical system according to Example 8 and aberration diagrams illustrating spherical aberration (SA), astigmatism (AS), distortion (DT), and lateral chromatic aberration (CC). 実施例９に係る斜視対物光学系の断面構成を示す図と、球面収差（ＳＡ）、非点収差（ＡＳ）、歪曲収差（ＤＴ）及び倍率色収差（ＣＣ）をそれぞれ示す収差図である。FIG. 10 is a diagram illustrating a cross-sectional configuration of a perspective objective optical system according to Example 9, and aberration diagrams illustrating spherical aberration (SA), astigmatism (AS), distortion (DT), and lateral chromatic aberration (CC). 実施例１０に係る斜視対物光学系の断面構成を示す図と、球面収差（ＳＡ）、非点収差（ＡＳ）、歪曲収差（ＤＴ）及び倍率色収差（ＣＣ）をそれぞれ示す収差図である。FIG. 10 is a diagram illustrating a cross-sectional configuration of a perspective objective optical system according to Example 10 and aberration diagrams illustrating spherical aberration (SA), astigmatism (AS), distortion (DT), and lateral chromatic aberration (CC). 実施例１１に係る斜視対物光学系の断面構成を示す図と、球面収差（ＳＡ）、非点収差（ＡＳ）、歪曲収差（ＤＴ）及び倍率色収差（ＣＣ）をそれぞれ示す収差図である。FIG. 10 is a diagram illustrating a cross-sectional configuration of a perspective objective optical system according to Example 11 and aberration diagrams illustrating spherical aberration (SA), astigmatism (AS), distortion (DT), and lateral chromatic aberration (CC). 実施例１２に係る斜視対物光学系の断面構成を示す図と、球面収差（ＳＡ）、非点収差（ＡＳ）、歪曲収差（ＤＴ）及び倍率色収差（ＣＣ）をそれぞれ示す収差図である。FIG. 14 is a diagram illustrating a cross-sectional configuration of a perspective objective optical system according to Example 12 and aberration diagrams illustrating spherical aberration (SA), astigmatism (AS), distortion (DT), and lateral chromatic aberration (CC). 実施例１３に係る斜視対物光学系の断面構成を示す図と、球面収差（ＳＡ）、非点収差（ＡＳ）、歪曲収差（ＤＴ）及び倍率色収差（ＣＣ）をそれぞれ示す収差図である。FIG. 14 is a diagram illustrating a cross-sectional configuration of a perspective objective optical system according to Example 13 and aberration diagrams illustrating spherical aberration (SA), astigmatism (AS), distortion (DT), and lateral chromatic aberration (CC). 実施例１４に係る斜視対物光学系の断面構成を示す図と、球面収差（ＳＡ）、非点収差（ＡＳ）、歪曲収差（ＤＴ）及び倍率色収差（ＣＣ）をそれぞれ示す収差図である。FIG. 18 is a diagram illustrating a cross-sectional configuration of a perspective objective optical system according to Example 14 and aberration diagrams illustrating spherical aberration (SA), astigmatism (AS), distortion (DT), and lateral chromatic aberration (CC). 実施例１５に係る斜視対物光学系の断面構成を示す図と、球面収差（ＳＡ）、非点収差（ＡＳ）、歪曲収差（ＤＴ）及び倍率色収差（ＣＣ）をそれぞれ示す収差図である。FIG. 18 is a diagram illustrating a cross-sectional configuration of a perspective objective optical system according to Example 15 and aberration diagrams illustrating spherical aberration (SA), astigmatism (AS), distortion (DT), and lateral chromatic aberration (CC). 内視鏡装置の構成を示す図である。It is a figure which shows the structure of an endoscope apparatus.
　以下、本実施形態に係る斜視対物光学系について、図面を用いて、このような構成をとった理由と作用を説明する。なお、以下の実施形態係る斜視対物光学系によりこの発明が限定されるものではない。 Hereinafter, the reason and action of the configuration of the perspective objective optical system according to this embodiment will be described with reference to the drawings. In addition, this invention is not limited by the perspective objective optical system which concerns on the following embodiment.
　本実施形態の斜視対物光学系は、物体側から順に、負レンズからなる前側レンズ群と、光路変換素子と、明るさ絞りと、正の屈折力を有する後側レンズ群と、から構成され、後側レンズ群は、正レンズと、正の屈折力を有する接合レンズと、からなり、接合レンズは、物体側から順に、正レンズと負レンズとで構成されている。 The perspective objective optical system of the present embodiment is composed of, in order from the object side, a front lens group including a negative lens, an optical path conversion element, an aperture stop, and a rear lens group having a positive refractive power. The rear lens group includes a positive lens and a cemented lens having a positive refractive power, and the cemented lens includes a positive lens and a negative lens in order from the object side.
　明るさ絞りの近傍、すなわち、明るさ絞りの物体側又は明るさ絞りの像側に光路変換素子を配置することで、光路変換素子における光線高を低く抑えることができる。その結果、光路変換素子のサイズを小さくできる。 By arranging the optical path conversion element in the vicinity of the aperture stop, that is, on the object side of the brightness stop or the image side of the aperture stop, the light beam height in the optical path conversion element can be kept low. As a result, the size of the optical path conversion element can be reduced.
　しかしながら、明るさ絞りよりも像側に光路変換素子を配置すると、明るさ絞りから像面までの距離は、少なくとも光路変換素子の硝路長分だけ長くなってしまう。そうすると、斜視対物光学系から出射する光線は、撮像素子の受光面に対してほぼ垂直になる。そのため、斜視対物光学系から出射する光線の角度は、撮像素子の斜入射特性を満足する角度にならない。その結果、画像の周辺部に、明るさのムラや色のムラが発生してしまう。 However, when the optical path conversion element is disposed on the image side of the aperture stop, the distance from the aperture stop to the image plane becomes longer by at least the glass path length of the optical path conversion element. If it does so, the light ray radiate | emitted from a perspective objective optical system will become substantially perpendicular | vertical with respect to the light-receiving surface of an image pick-up element. Therefore, the angle of the light beam emitted from the oblique objective optical system does not satisfy the oblique incident characteristic of the image sensor. As a result, brightness unevenness and color unevenness occur in the peripheral portion of the image.
　また、斜視対物光学系の組立てでは、ピント調整を行う。そのため、無理に撮像素子の斜入射特性を満足させようとすると、ピント調整に必要な間隔が不足する。また、斜入射特性に合わせて無理に光線を曲げることになるので、収差が発生してしまう。その結果、著しく光学性能が低下してしまう。 Also, focus adjustment is performed when assembling the perspective objective optical system. For this reason, if an attempt is made to satisfy the oblique incident characteristics of the image sensor, the interval necessary for focus adjustment is insufficient. Further, since the light beam is forcibly bent in accordance with the oblique incidence characteristic, an aberration occurs. As a result, the optical performance is significantly deteriorated.
　そこで、本実施形態に係る斜視対物光学系では、明るさ絞りよりも物体側に光路変換素子を配置している。これにより、明るさ絞りから像面までの距離を短くできるので、斜視対物光学系から出射する光線の角度を、撮像素子の斜入射特性を満足する角度にすることが、比較的容易に行える。 Therefore, in the perspective objective optical system according to the present embodiment, the optical path conversion element is arranged on the object side of the aperture stop. Thereby, since the distance from the aperture stop to the image plane can be shortened, it is relatively easy to set the angle of the light beam emitted from the oblique objective optical system to an angle that satisfies the oblique incidence characteristics of the image sensor.
　更に、明るさ絞りよりも物体側では硝路長が長くなる。そのため、前側レンズ群を保持する枠部材の長さを、適切に確保することができる。その結果、斜視対物光学系の組立てや、斜視対物光学系の内視鏡先端部への取り付けを、高精度で容易に行うことができる。 Furthermore, the glass path length is longer on the object side than the aperture stop. Therefore, the length of the frame member that holds the front lens group can be appropriately ensured. As a result, assembly of the perspective objective optical system and attachment of the perspective objective optical system to the distal end portion of the endoscope can be easily performed with high accuracy.
　接合レンズは、物体側から順に、正レンズと負レンズとで構成されていることが望ましい。このようにすることで、斜視対物光学系を小型化することができる。また、斜視対物光学系から出射する光線の角度を、撮像素子の斜入射特性を満足する角度にすることができる。 The cemented lens is preferably composed of a positive lens and a negative lens in order from the object side. By doing in this way, a perspective objective optical system can be reduced in size. In addition, the angle of the light beam emitted from the oblique objective optical system can be set to an angle that satisfies the oblique incident characteristics of the image sensor.
　接合レンズを、物体側から順に、負レンズと正レンズとで構成すると、接合レンズにおける光線高が高くなってしまうので、レンズの外径が大きくなる。そのため、レンズの加工性が悪くなる。また、斜視対物光学系全体としても外径が大きくなってしまう。 If the cemented lens is composed of a negative lens and a positive lens in this order from the object side, the height of the light beam at the cemented lens increases, and the outer diameter of the lens increases. Therefore, the processability of the lens is deteriorated. Also, the outer diameter of the entire perspective objective optical system becomes large.
　更に、像側に配置した正レンズの作用によって光線が曲げられるため、斜視対物光学系から出射する光線が、撮像素子の受光面に対してほぼ垂直になる。その結果、斜視対物光学系から出射する光線の角度を、撮像素子の斜入射特性を満足する角度にすることが難しくなる。無理に斜入射特性を満足する角度にしようとすると、接合レンズ面で光線が大きく曲げられるので収差が発生する。そのため、光学性能が劣化してしまう。 Furthermore, since the light beam is bent by the action of the positive lens arranged on the image side, the light beam emitted from the oblique objective optical system becomes almost perpendicular to the light receiving surface of the image sensor. As a result, it becomes difficult to set the angle of the light beam emitted from the oblique objective optical system to an angle that satisfies the oblique incidence characteristics of the image sensor. Forcing the angle to satisfy the oblique incidence characteristic causes aberrations because the light rays are greatly bent at the cemented lens surface. Therefore, the optical performance is deteriorated.
　本実施形態の斜視対物光学系は、上記の構成を備えると共に、以下の条件式（１）、（２）を満足する。
　－２．０＜ｆF／ｆ＜－１．３　　　（１）
　１．７＜ｆR／ｆ＜２．７　　　（２）
　ここで、
　ｆFは、前側レンズ群の焦点距離、
　ｆRは、後側レンズ群の焦点距離、
　ｆは、斜視対物光学系全系の焦点距離、
である。 The perspective objective optical system of the present embodiment has the above configuration and satisfies the following conditional expressions (1) and (2).
-2.0 <f F /f<-1.3 (1)
1.7 <f R /f<2.7 (2)
here,
f F is the focal length of the front lens group,
f R is the focal length of the rear lens group,
f is the focal length of the entire oblique objective optical system,
It is.
　条件式（１）は、前側レンズ群の焦点距離を規定した条件式である。 Conditional expression (1) is a conditional expression that defines the focal length of the front lens group.
　条件式（１）の下限値を下回ると、前側レンズ群の屈折力が小さくなるため、斜視対物光学系の画角が小さくなる。この状態で大きな画角を確保しようとすると、前側レンズ群の負レンズ（以下、「前側負レンズ」という）から明るさ絞りまでの距離が長くなってしまう。そうすると、前側負レンズから明るさ絞りまでの間の光線高が高くなるため、前側負レンズが大型化すると共に、光学系全体が大型化してしまう。 When the lower limit value of conditional expression (1) is not reached, the refractive power of the front lens group becomes small, so the angle of view of the perspective objective optical system becomes small. If a large angle of view is to be secured in this state, the distance from the negative lens in the front lens group (hereinafter referred to as “front negative lens”) to the aperture stop becomes long. As a result, the height of the light beam from the front negative lens to the aperture stop becomes high, which increases the size of the front negative lens and the size of the entire optical system.
　条件式（１）の上限値を上回ると、前側レンズ群の屈折力が大きくなるため、斜視対物光学系の画角が大きくなる。画角が大きくなると、レンズを通過する光線の高さが高くなるためレンズ外径が大きくなってしまう。更に、画角が大きくなることで観察画像の周辺部が暗くなってしまう。画像周辺部を明るくするためには更に照明光を明るくしなければならないが、そうすると照明光学系の大型化を招いてしまう。いずれも内視鏡の細径化には好ましくない。 If the upper limit value of conditional expression (1) is exceeded, the refractive power of the front lens unit increases, so the angle of view of the perspective objective optical system increases. As the angle of view increases, the height of the light beam passing through the lens increases, and the outer diameter of the lens increases. Furthermore, the peripheral portion of the observation image becomes dark as the angle of view increases. In order to brighten the peripheral portion of the image, it is necessary to further brighten the illumination light. However, this would increase the size of the illumination optical system. Neither is preferred for reducing the diameter of an endoscope.
　更に、前側レンズ群の屈折力が大きくなると、前側負レンズの曲率半径が小さくなるため、レンズの加工が難しくなる。更に、前側負レンズの屈折力が大きくなることで、特に、レンズが偏心した場合に光学性能の劣化が大きくなる。その結果、安定した光学性能をもつ斜視対物光学系を実現することが困難になる。 Furthermore, when the refractive power of the front lens group increases, the radius of curvature of the front negative lens decreases, making it difficult to process the lens. Furthermore, since the refractive power of the front negative lens is increased, the deterioration of the optical performance is increased particularly when the lens is decentered. As a result, it becomes difficult to realize a perspective objective optical system having stable optical performance.
　条件式（２）は、後側レンズ群の焦点距離を規定した条件式である。 Conditional expression (2) is a conditional expression that defines the focal length of the rear lens group.
　条件式（２）の下限値を下回ると、後側レンズ群の屈折力が大きくなるため、像位置が後側レンズ群に近づき過ぎてしまう。そうすると、ピント調整に必要な間隔が狭くなってしまうので、ピント調整に必要な間隔が不足する。そのため、遠点側の深度が、本来必要とする深度よりも浅くなる。 If the lower limit value of conditional expression (2) is not reached, the refractive power of the rear lens unit increases, and the image position becomes too close to the rear lens unit. As a result, the interval necessary for focus adjustment becomes narrow, and the interval necessary for focus adjustment is insufficient. For this reason, the depth on the far point side is shallower than the originally required depth.
　更に、後側レンズ群の屈折力が大きくなると、後側レンズ群を構成する各レンズの屈折力も大きくなる。この場合、各レンズの曲率半径が小さくなるので、レンズの加工が難しくなる。 Furthermore, as the refractive power of the rear lens group increases, the refractive power of each lens constituting the rear lens group also increases. In this case, since the radius of curvature of each lens becomes small, it becomes difficult to process the lens.
　条件式（２）の上限値を上回ると、後側レンズ群の屈折力が小さくなるため、像位置が後側レンズ群から離れ過ぎてしまう。この場合、明るさ絞りから像位置までの硝路長が長くなるので、光学系全体が大型化する。 If the upper limit value of conditional expression (2) is exceeded, the refractive power of the rear lens group becomes small, so that the image position is too far from the rear lens group. In this case, since the glass path length from the aperture stop to the image position becomes long, the entire optical system becomes large.
　条件式（１）と条件式（２）を満足することによって、本実施形態に係る斜視対物光学系では、前側レンズ群の屈折力と後側レンズ群の屈折力とのバランスを最適にすることができる。その結果、諸収差が良好に補正された斜視対物光学系を実現することができる。 By satisfying conditional expression (1) and conditional expression (2), in the perspective objective optical system according to this embodiment, the balance between the refractive power of the front lens group and the refractive power of the rear lens group is optimized. Can do. As a result, a perspective objective optical system in which various aberrations are favorably corrected can be realized.
　条件式（１）に代えて、以下の条件式（１’）を満足することが好ましい。
　－１．９＜ｆF／ｆ＜－１．４　　　（１’）
　条件式（２）に代えて、以下の条件式（２’）を満足することが好ましい。
　１．８＜ｆR／ｆ＜２．５　　　（２’） It is preferable to satisfy the following conditional expression (1 ′) instead of conditional expression (1).
−1.9 <f F /f<−1.4 (1 ′)
It is preferable to satisfy the following conditional expression (2 ′) instead of conditional expression (2).
1.8 <f R /f<2.5 (2 ′)
　更に、本実施形態の斜視対物光学系は、以下の条件式（３）を満足する。
　０．６３＜｜ｆF／ｆR｜＜０．８８　　　（３）
　ここで、
　ｆFは、前側レンズ群の焦点距離、
　ｆRは、後側レンズ群の焦点距離、
である。 Furthermore, the perspective objective optical system of the present embodiment satisfies the following conditional expression (3).
0.63 <| f F / f R | <0.88 (3)
here,
f F is the focal length of the front lens group,
f R is the focal length of the rear lens group,
It is.
　条件式（３）は、前側レンズ群の焦点距離と後側レンズ群の焦点距離の比を規定した条件式である。条件式（３）を満足することで、前側レンズ群の屈折力と後側レンズ群の屈折力のバランスを最適にすることができる。その結果、諸収差が良好に補正された斜視対物光学系を実現することができる。 Conditional expression (3) is a conditional expression that defines the ratio of the focal length of the front lens group and the focal length of the rear lens group. By satisfying conditional expression (3), the balance between the refractive power of the front lens group and the refractive power of the rear lens group can be optimized. As a result, a perspective objective optical system in which various aberrations are favorably corrected can be realized.
　条件式（３）の下限値を下回ると、前側レンズ群の焦点距離が短くなる（前側レンズ群の屈折力が大きくなる）。そのため、斜視対物光学系の画角が大きくなる。画角が大きくなると、レンズを通過する光線の高さが高くなるためレンズ外径が大きくなってしまう。更に、画角が大きくなることで観察画像の周辺部が暗くなってしまう。画像周辺部を明るくするためには更に照明光を明るくしなければならないが、そうすると照明光学系の大型化を招いてしまう。いずれも内視鏡の細径化には好ましくない。 When the lower limit value of conditional expression (3) is not reached, the focal length of the front lens unit is shortened (the refractive power of the front lens unit is increased). Therefore, the angle of view of the perspective objective optical system is increased. As the angle of view increases, the height of the light beam passing through the lens increases, and the outer diameter of the lens increases. Furthermore, the peripheral portion of the observation image becomes dark as the angle of view increases. In order to brighten the peripheral portion of the image, it is necessary to further brighten the illumination light. However, this would increase the size of the illumination optical system. Neither is preferred for reducing the diameter of an endoscope.
　更に、前側負レンズの屈折力が、後側レンズ群の正の屈折力よりも大きくなる。そのため、負の屈折力の影響を受ける収差を、後側レンズ群で十分に補正することができない。その結果、正方向に像面湾曲が生じる。 Furthermore, the refractive power of the front negative lens is greater than the positive refractive power of the rear lens group. Therefore, the aberration that is affected by the negative refractive power cannot be sufficiently corrected by the rear lens group. As a result, field curvature occurs in the positive direction.
　更に、前側レンズ群の屈折力と後側レンズ群の屈折力とのバランスが悪くなる。この場合、非点収差の発生量が大きくなるので、特に、子午線方向の像面が大きく正方向に傾いてしまう。そのため、レンズが偏心した場合に、画像に片ボケが発生しやすくなる。特に、近点観察時に、画像の周辺部が著しくボケてしまう虞がある。 Furthermore, the balance between the refractive power of the front lens group and the refractive power of the rear lens group becomes worse. In this case, the amount of astigmatism increases, and in particular, the image plane in the meridian direction is greatly tilted in the positive direction. Therefore, when the lens is decentered, one-side blur tends to occur in the image. In particular, there is a risk that the peripheral portion of the image will be significantly blurred during near-point observation.
　条件式（３）の上限値を上回ると、前側レンズ群の焦点距離が長くなる（前側レンズ群の屈折力が小さくなる）。そのため、斜視対物光学系の画角が小さくなる。 If the upper limit of conditional expression (3) is exceeded, the focal length of the front lens group becomes longer (the refractive power of the front lens group becomes smaller). Therefore, the angle of view of the perspective objective optical system is reduced.
　更に、前側負レンズの屈折力が、後側レンズ群の正の屈折力よりも小さくなる。そのため、後側レンズ群による補正が、負の屈折力の影響を受ける収差に対して過剰になる。その結果、負方向に大きな像面湾曲が生じる。 Furthermore, the refractive power of the front negative lens is smaller than the positive refractive power of the rear lens group. For this reason, correction by the rear lens unit becomes excessive for aberrations that are affected by negative refractive power. As a result, a large curvature of field occurs in the negative direction.
　更に、前側レンズ群の屈折力と後側レンズ群の屈折力とのバランスが悪くなる。この場合、非点収差の発生量が大きくなるので、特に、子午線方向の像面が大きく負方向に傾いてしまう。そのため、レンズが偏心した場合に、画像に片ボケが発生しやすくなる。特に、遠点観察時に、画像の周辺部が著しくボケてしまう虞がある。 Furthermore, the balance between the refractive power of the front lens group and the refractive power of the rear lens group becomes worse. In this case, since the amount of astigmatism generated becomes large, the image plane in the meridian direction is particularly inclined in the negative direction. Therefore, when the lens is decentered, one-side blur tends to occur in the image. In particular, the peripheral portion of the image may be significantly blurred during far-point observation.
　また、本実施形態の斜視対物光学系は、以下の条件式（４）、（５）を満足することが好ましい。
　２．４＜Ｄ１／ｆ＜４．４　　　（４）
　１．１＜Ｄ２／ｆ＜１．７　　　（５）
　ここで、
　Ｄ１は、前側レンズ群の負レンズの像側面から明るさ絞りまでの空気換算長、
　Ｄ２は、後側レンズ群の最終レンズの像側面から像面までの空気換算長、
　ｆは、斜視対物光学系全系の焦点距離、
である。 Moreover, it is preferable that the perspective objective optical system of this embodiment satisfies the following conditional expressions (4) and (5).
2.4 <D1 / f <4.4 (4)
1.1 <D2 / f <1.7 (5)
here,
D1 is the air equivalent length from the image side surface of the negative lens of the front lens group to the aperture stop,
D2 is the air equivalent length from the image side surface to the image surface of the final lens in the rear lens group,
f is the focal length of the entire oblique objective optical system,
It is.
　条件式（４）は前側レンズ群の負レンズの像側面から明るさ絞りまでの空気換算長を規定した条件式である。例えば、後述の実施例１では、Ｄ１は以下の式で求まる。
　Ｄ１＝ｄ２＋ｄ３／ｎ３＋ｄ４＋ｄ５／ｎ５ Conditional expression (4) is a conditional expression that defines the air-converted length from the image side surface of the negative lens of the front lens group to the aperture stop. For example, in Example 1 described later, D1 is obtained by the following equation.
D1 = d2 + d3 / n3 + d4 + d5 / n5
　条件式（４）の下限値を下回ると、最適な外径形状の光路変換素子を配置するためのスペースを十分に確保することが難しくなる。そのため、光路変換素子で、光線のけられが発生する。また、光路変換素子の光学面以外に光線が入射することで、画像にフレアが発生する虞がある。 If the lower limit value of conditional expression (4) is not reached, it is difficult to ensure a sufficient space for arranging the optical path conversion element having the optimum outer diameter shape. For this reason, the optical path conversion element causes light beam shifting. Moreover, there is a possibility that flare may occur in an image when light rays enter other than the optical surface of the optical path conversion element.
　また、前側レンズ群を保持する枠部材の長さを、適切に確保することが難しくなる。この場合、組立用の治工具に枠部材を安定的に保持することができなくなる。そのため、斜視対物光学系の組立てやピント調整を、高精度に行うことが難しくなる。更に、斜視対物光学系の内視鏡先端部への取り付けと固定を、高精度に行うことが難しくなる。 Also, it is difficult to appropriately secure the length of the frame member that holds the front lens group. In this case, the frame member cannot be stably held on the jig for assembly. Therefore, it becomes difficult to assemble the perspective objective optical system and adjust the focus with high accuracy. Furthermore, it becomes difficult to attach and fix the oblique objective optical system to the distal end portion of the endoscope with high accuracy.
　条件式（４）の上限値を上回ると、光路変換素子を配置するためのスペースを十分に確保できるが、前側負レンズから明るさ絞りまでの硝路長が長くなりすぎる。この場合、前側負レンズにおける光線高が高くなるので、前側負レンズの外径が大きくなる。これに伴って、斜視対物光学系が大型化する。更に、斜視対物光学系の大型化に伴って、それを搭載する内視鏡の外径も大きくなる。 If the upper limit value of conditional expression (4) is exceeded, a sufficient space for arranging the optical path conversion element can be secured, but the glass path length from the front negative lens to the aperture stop becomes too long. In this case, the height of the light beam in the front negative lens increases, so the outer diameter of the front negative lens increases. Along with this, the perspective objective optical system becomes larger. Furthermore, as the perspective objective optical system increases in size, the outer diameter of the endoscope on which it is mounted also increases.
　条件式（５）は後側レンズ群の最終レンズの像側面から像面までの空気換算長を規定した条件式である。ここで、最終レンズは屈折力を有するレンズを意味する。よって、カラーフィルタ等の平行平板フィルタやパワーレスレンズは、最終レンズではない。例えば、後述の実施例１では、Ｄ２は以下の式で求まる。
　Ｄ２＝ｄ１４＋ｄ１５／ｎ１５＋ｄ１６／ｎ１６＋ｄ１７／ｎ１７ Conditional expression (5) is a conditional expression that defines the air-converted length from the image side surface to the image surface of the final lens in the rear lens group. Here, the final lens means a lens having refractive power. Therefore, a parallel plate filter such as a color filter or a powerless lens is not the final lens. For example, in Example 1 described later, D2 is obtained by the following equation.
D2 = d14 + d15 / n15 + d16 / n16 + d17 / n17
　条件式（５）の下限値を下回ると、最終レンズから像面までの間隔が狭くなり過ぎる。この場合、撮像素子と斜視対物光学系との間隔が狭くなり過ぎるので、斜視対物光学系の組立時に十分なピント調整が行えない。そのため、遠点側の深度が、本来必要とする深度よりも浅くなる。 If the lower limit of conditional expression (5) is not reached, the distance from the final lens to the image plane becomes too narrow. In this case, since the distance between the imaging element and the perspective objective optical system becomes too narrow, sufficient focus adjustment cannot be performed when the perspective objective optical system is assembled. For this reason, the depth on the far point side is shallower than the originally required depth.
　条件式（５）の上限値を上回ると、最終レンズから像面までの距離を十分に確保できるため、斜視対物光学系の組立時のピント調整はできる。しかしながら、最終レンズから像面までの距離が長くなり過ぎるため、撮像素子の位置が斜視対物光学系から離れ過ぎてしまう。その結果、斜視対物光学系を内視鏡先端部に取り付けた時に、斜視対物光学系と撮像素子（以下、「撮像系」という）が、他の部材と干渉しやすくなる。この干渉を避けるためには、内視鏡内の撮像系の周囲にクリアランスを設ける必要がある。そうすると、内視鏡先端部全体が大型化してしまう。 If the upper limit of conditional expression (5) is exceeded, a sufficient distance from the final lens to the image plane can be secured, so that the focus adjustment during assembly of the perspective objective optical system can be performed. However, since the distance from the final lens to the image plane becomes too long, the position of the image sensor is too far from the perspective objective optical system. As a result, when the oblique objective optical system is attached to the distal end portion of the endoscope, the oblique objective optical system and the imaging element (hereinafter referred to as “imaging system”) are likely to interfere with other members. In order to avoid this interference, it is necessary to provide a clearance around the imaging system in the endoscope. If it does so, the whole endoscope front-end | tip part will enlarge.
　条件式（４）に代えて、以下の条件式（４’）を満足することが好ましい。
　２．４＜Ｄ１／ｆ＜４．２　　　（４’）
　条件式（５）に代えて、以下の条件式（５’）を満足することが好ましい。
　１．１＜Ｄ２／ｆ＜１．６　　　（５’） It is preferable to satisfy the following conditional expression (4 ′) instead of conditional expression (4).
2.4 <D1 / f <4.2 (4 ′)
It is preferable to satisfy the following conditional expression (5 ′) instead of conditional expression (5).
1.1 <D2 / f <1.6 (5 ′)
　また、本実施形態の斜視対物光学系は、以下の条件式（６）を満足することが好ましい。
　１．７＜Ｄ１／Ｄ２＜３．１　　　（６）
　ここで、
　Ｄ１は、前側レンズ群の負レンズの像側面から明るさ絞りまでの空気換算長、
　Ｄ２は、後側レンズ群の最終レンズの像側面から像面までの空気換算長、
である。 Moreover, it is preferable that the perspective objective optical system of this embodiment satisfies the following conditional expression (6).
1.7 <D1 / D2 <3.1 (6)
here,
D1 is the air equivalent length from the image side surface of the negative lens of the front lens group to the aperture stop,
D2 is the air equivalent length from the image side surface to the image surface of the final lens in the rear lens group,
It is.
　条件式（６）は、前側レンズ群の負レンズの像側面から明るさ絞りまでの空気換算長と、後側レンズ群の最終レンズの像側面から像面までの空気換算長と、の比を規定した条件式である。条件式（６）を満足することで、２つの空気換算長のバランスを最適にすることができる。その結果、特に、撮像系のサイズを最適にすることができる。 Conditional expression (6) is the ratio of the air-converted length from the image side surface of the negative lens in the front lens unit to the aperture stop and the air-converted length from the image side surface of the final lens in the rear lens unit to the image surface. It is a defined conditional expression. By satisfying conditional expression (6), the balance between the two air conversion lengths can be optimized. As a result, in particular, the size of the imaging system can be optimized.
　条件式（６）の下限値を下回ると、前側レンズ群の負レンズの像側面から明るさ絞りまでの空気換算長が短くなり過ぎる。この場合、枠部材を組立用の治工具で保持しにくくなるので、組立性が悪くなる。 If the lower limit of conditional expression (6) is not reached, the air equivalent length from the image side surface of the negative lens in the front lens group to the aperture stop becomes too short. In this case, since it becomes difficult to hold the frame member with the jig for assembly, the assemblability deteriorates.
　条件式（６）の上限値を上回ると、枠部材が大型化する。特に、前側レンズ群を保持する枠部材の大型化を招くため、内視鏡先端部の外径が大きくなる。 If the upper limit value of conditional expression (6) is exceeded, the frame member becomes larger. In particular, since the frame member that holds the front lens group is increased in size, the outer diameter of the endoscope distal end is increased.
　また、本実施形態の斜視対物光学系は、以下の条件式（７）を満足することが好ましい。
　１．５＜ｆ3／ｆ2＜３．１　　　（７）
　ここで、
　ｆ2は、後側レンズ群の正レンズの焦点距離、
　ｆ3は、後側レンズ群の接合レンズの焦点距離、
である。 Moreover, it is preferable that the perspective objective optical system of this embodiment satisfies the following conditional expression (7).
1.5 <f 3 / f 2 <3.1 (7)
here,
f 2 is the focal length of the positive lens in the rear lens group,
f 3 is the focal length of the cemented lens in the rear lens group,
It is.
　条件式（７）は後側レンズ群の正レンズの焦点距離と後側レンズ群の接合レンズの焦点距離を規定した条件式である。条件式（７）を満足することで、正レンズの屈折力と接合レンズの屈折力とのバランスを最適にすることができる。 Conditional expression (7) is a conditional expression that defines the focal length of the positive lens in the rear lens group and the focal length of the cemented lens in the rear lens group. By satisfying conditional expression (7), the balance between the refractive power of the positive lens and the refractive power of the cemented lens can be optimized.
　条件式（７）の下限値を下回ると、接合レンズの焦点距離が短くなるので、後側レンズ群における正の屈折力が大きくなる、この場合、像位置が後側レンズ群に近づき過ぎてしまう。そのため、ピント調整に必要な間隔が不足する。その結果、遠点側の深度が、本来必要とする深度よりも浅くなる。また、像の周辺部においてコマ収差の発生量が大きくなるので、光学性能が低下する。 If the lower limit value of the conditional expression (7) is not reached, the focal length of the cemented lens is shortened, so that the positive refractive power in the rear lens group is increased. In this case, the image position is too close to the rear lens group. . Therefore, the interval necessary for focus adjustment is insufficient. As a result, the depth on the far point side becomes shallower than the originally required depth. In addition, since the amount of coma generated at the periphery of the image is increased, the optical performance is degraded.
　更に、特に、後側レンズ群において、正レンズ全体の屈折力と負レンズ全体の屈折力とのバランスが崩れる。その結果、軸上色収差と倍率色収差が発生する。そのため、光学性能が低下する。 Furthermore, particularly in the rear lens group, the balance between the refractive power of the entire positive lens and the refractive power of the entire negative lens is lost. As a result, axial chromatic aberration and lateral chromatic aberration are generated. Therefore, the optical performance is deteriorated.
　条件式（７）の上限値を上回ると、接合レンズの焦点距離が長くなるので、後側レンズ群における正の屈折力が小さくなる。この場合、像位置が後側レンズ群から離れ過ぎてしまう。そのため、光学系の全長が長くなる。また、像の周辺部においてコマ収差の発生量が大きくなるので、光学性能が低下する。 If the upper limit value of conditional expression (7) is exceeded, the focal length of the cemented lens becomes longer, so the positive refractive power in the rear lens group becomes smaller. In this case, the image position is too far from the rear lens group. Therefore, the total length of the optical system becomes long. In addition, since the amount of coma generated at the periphery of the image is increased, the optical performance is degraded.
　更に、特に、後側レンズ群において、正レンズ全体の屈折力と負レンズ全体の屈折力のバランスが崩れる。その結果、軸上色収差と倍率色収差が発生する。そのため、光学性能が低下する。 Furthermore, particularly in the rear lens group, the balance between the refractive power of the entire positive lens and the refractive power of the entire negative lens is lost. As a result, axial chromatic aberration and lateral chromatic aberration are generated. Therefore, the optical performance is deteriorated.
　また、本実施形態の斜視対物光学系は、以下の条件式（８）を満足することが好ましい。
　１．１＜|Ｒc|／ｆ＜２．１　　　（８）
　ここで、
　Ｒcは、後側レンズ群の接合レンズの接合面の曲率半径、
　ｆは、斜視対物光学系全系の焦点距離、
である。 Moreover, it is preferable that the perspective objective optical system of this embodiment satisfies the following conditional expression (8).
1.1 <| R c | / f <2.1 (8)
here,
R c is the radius of curvature of the cemented surface of the cemented lens in the rear lens group,
f is the focal length of the entire oblique objective optical system,
It is.
　条件式（８）の下限値を下回ると、接合レンズの接合面の曲率半径が小さくなる。この場合、接合レンズの正レンズでは縁肉が少なくなってしまい、また、接合レンズの負レンズでは球欠面が深くなってしまう。そのため、レンズの加工性が悪くなる。 If the lower limit of conditional expression (8) is not reached, the radius of curvature of the cemented lens cemented surface becomes small. In this case, the thickness of the positive lens of the cemented lens is reduced, and the spherical surface of the negative lens of the cemented lens is deepened. Therefore, the processability of the lens is deteriorated.
　条件式（８）の上限値を上回ると、接合レンズの接合面の曲率半径が大きくなる。この場合、接合面の屈折力が小さくなるので、色収差の補正が困難になる。 If the upper limit of conditional expression (8) is exceeded, the radius of curvature of the cemented lens cemented surface increases. In this case, since the refractive power of the cemented surface becomes small, it becomes difficult to correct chromatic aberration.
　条件式（８）では、Ｒcを絶対値で規定しているが、Ｒcの値は負の値であることが望ましい。 In conditional expression (8), R c is defined as an absolute value, but the value of R c is preferably a negative value.
　また、本実施形態の斜視対物光学系は、以下の条件式（９）を満足することが好ましい。
　－１７°＜ＴＷ＜０°　　　（９）
　ここで、
　ＴＷは、最大像高時の像面への光線入射角度、
である。 Moreover, it is preferable that the perspective objective optical system of this embodiment satisfies the following conditional expression (9).
-17 ° <TW <0 ° (9)
here,
TW is the light incident angle on the image plane at the maximum image height,
It is.
　条件式（９）を満足することで、後側レンズ群における光線高を低く抑えることができる。そのため、後側レンズ群におけるレンズの外径を小さくできる。加えて、枠部材も含めた状態で後側レンズ群を小型化できる。 Satisfying conditional expression (9) makes it possible to keep the light beam height in the rear lens group low. Therefore, the outer diameter of the lens in the rear lens group can be reduced. In addition, the rear lens group can be reduced in size with the frame member included.
　なお、ＴＷは、最大像高に到達する主光線と光軸に平行な軸とのなす角度である。角度の正負は、最大像高に到達する主光線が光軸に対して徐々に離れて入射する場合を負とする。また、ＴＷは、媒質が空気中のときの角度である。 Note that TW is an angle formed between a principal ray reaching the maximum image height and an axis parallel to the optical axis. The sign of the angle is negative when the chief ray that reaches the maximum image height enters the optical axis gradually away from the optical axis. TW is an angle when the medium is in the air.
　条件式（９）に代えて、以下の条件式（９’）を満足することが好ましい。
　－１２°≦ＴＷ≦－５°　　　（９’） It is preferable to satisfy the following conditional expression (9 ′) instead of conditional expression (9).
−12 ° ≦ TW ≦ −5 ° (9 ')
　また、本実施形態の斜視対物光学系では、光路変換素子は、プリズム又はミラーであることが好ましい。 Further, in the perspective objective optical system of the present embodiment, the optical path conversion element is preferably a prism or a mirror.
　また、本実施形態の斜視対物光学系では、光路変換素子に、高屈折率硝材を使用することができる。 In the perspective objective optical system of the present embodiment, a high refractive index glass material can be used for the optical path conversion element.
　上述のように、本実施形態に係る斜視対物光学系では、明るさ絞りよりも物体側に光路変換素子を配置している。この構成により、前側レンズ群を保持する枠部材の長さを、適切に確保することができている。ただし、この構成では、特に、前側負レンズにおいて光線高が高くなるので、前側負レンズの外径が大きくなりやすい。 As described above, in the perspective objective optical system according to the present embodiment, the optical path conversion element is arranged on the object side of the aperture stop. With this configuration, the length of the frame member that holds the front lens group can be appropriately secured. However, with this configuration, the height of the light beam is particularly high in the front negative lens, so the outer diameter of the front negative lens tends to increase.
　そこで、光路変換素子に、高屈折率硝材を使用することが好ましい。このようにすることで、光路変換素子の空気換算長を短くできるので、前側負レンズにおける光線高を低く抑えることができる。 Therefore, it is preferable to use a high refractive index glass material for the optical path conversion element. By doing in this way, since the air conversion length of an optical path conversion element can be shortened, the light ray height in a front negative lens can be suppressed low.
　また、本実施形態の斜視対物光学系では、接合レンズの正レンズに低分散硝材を使用し、接合レンズの負レンズに高分散硝材を使用することができる。 In the perspective objective optical system of the present embodiment, a low dispersion glass material can be used for the positive lens of the cemented lens, and a high dispersion glass material can be used for the negative lens of the cemented lens.
　一般に、高屈折率硝材のアッベ数はあまり大きくないため、高屈折率硝材では分散が大きくなる。そのため、光路変換素子に高屈折率硝材を使用することで光路変換素子の空気換算長を短くできても、色収差への影響は残る。 Generally, since the Abbe number of a high refractive index glass material is not so large, dispersion becomes large in a high refractive index glass material. Therefore, even if the air conversion length of the optical path conversion element can be shortened by using a high refractive index glass material for the optical path conversion element, the influence on chromatic aberration remains.
　このようなことから、接合レンズの正レンズに低分散硝材を使用し、接合レンズの負レンズに高分散硝材を使用することが好ましい。特に、接合レンズの負レンズには、異常分散性を持つ硝材を用いると良い。このようにすることで、色収差を良好に補正することができる。更に、斜視対物光学系全体での諸収差を、バランスの取れた状態にすることができる。 For this reason, it is preferable to use a low dispersion glass material for the positive lens of the cemented lens and a high dispersion glass material for the negative lens of the cemented lens. In particular, a glass material having anomalous dispersion is preferably used for the negative lens of the cemented lens. In this way, chromatic aberration can be corrected satisfactorily. Further, various aberrations in the entire oblique objective optical system can be balanced.
　また、斜視対物光学系の画角は、主に前側負レンズの屈折力によって決まる。前側負レンズと明るさ絞りとの間には、硝路長の長い光路変換素子が配置されるので、前側負レンズにおける光線高が高くなる。そのため、負レンズの外径が大きくなって、対物光学系も大型化する。しかし、一方、前側負レンズの曲率半径が大きくなるため、前側負レンズが偏心しても片ボケなどが生じにくくなって、光学性能が低下しにくくなる。このため、レンズ外径だけでなく、レンズ偏心による光学性能への影響も考慮して、明るさ絞りから物体側の構成を最適な構成にする必要がある。 Also, the angle of view of the perspective objective optical system is mainly determined by the refractive power of the front negative lens. Since an optical path conversion element having a long glass path length is disposed between the front negative lens and the aperture stop, the light beam height at the front negative lens is increased. For this reason, the outer diameter of the negative lens increases and the objective optical system also increases in size. However, since the radius of curvature of the front negative lens is increased, even if the front negative lens is decentered, one-sided blur or the like is less likely to occur, and the optical performance is less likely to be deteriorated. For this reason, in consideration of not only the lens outer diameter but also the effect on the optical performance due to the lens decentering, it is necessary to optimize the configuration on the object side from the aperture stop.
　また、本実施形態の斜視用内視鏡は、上述の斜視対物光学系を備えることを特徴とする。 The perspective endoscope of the present embodiment is characterized by including the above-described perspective objective optical system.
　本実施形態の斜視対物光学系は、小型で高性能な斜視対物光学系である。よって、このような斜視対物光学系を備えることで、高画質の画像が得られると共に、細径化された先端部を有する斜視用内視鏡を実現することができる。 The perspective objective optical system of the present embodiment is a small and high-performance perspective objective optical system. Therefore, by providing such a perspective objective optical system, a high-quality image can be obtained, and a perspective endoscope having a thinned tip can be realized.
　また、本実施形態の斜視対物光学系は、内視鏡装置に用いることができる。内視鏡装置は、本実施形態の斜視対物光学系と、撮像素子と、を少なくとも備える。 Further, the perspective objective optical system of the present embodiment can be used for an endoscope apparatus. The endoscope apparatus includes at least the perspective objective optical system of the present embodiment and an image sensor.
　実施例の説明に先立って、本実施例の斜視対物光学系の概要について説明する。各実施例における斜視対物光学系の断面構成を示す図では、光路変換素子は、プリズムを展開した図として示されている。そのため、光路変換素子は、平行平面板として描かれている。 Prior to the description of the embodiment, an outline of the perspective objective optical system of the present embodiment will be described. In the drawings showing the cross-sectional configuration of the perspective objective optical system in each embodiment, the optical path conversion element is shown as a developed view of a prism. Therefore, the optical path conversion element is drawn as a parallel plane plate.
　展開されていない状態のプリズムの例を図６に示す。図６（ａ）はプリズムを展開しない状態で描いたときのレンズ断面図である。ここでは、本実施例の斜視対物光学系として、実施例１の斜視対物光学系が例示されている。本実施例の斜視対物光学系は、プリズムＰを介して配置された前側レンズ群ＧＦと後側レンズ群ＧＲとを有し、開口絞りＳはプリズムＰと後側レンズ群ＧＲとの間に配置されている。 Fig. 6 shows an example of a prism that is not expanded. FIG. 6A is a lens cross-sectional view when the prism is drawn without being developed. Here, the perspective objective optical system of Example 1 is illustrated as the perspective objective optical system of the present example. The perspective objective optical system of the present embodiment has a front lens group GF and a rear lens group GR disposed via a prism P, and an aperture stop S is disposed between the prism P and the rear lens group GR. Has been.
　すなわち、本実施例の斜視対物光学系は、プリズムＰの物体側に前側レンズ群ＧＦが配置され、プリズムＰの像側に後側レンズ群ＧＲが配置されている。前側レンズ群ＧＦは負の屈折力を有し、負の屈折力のレンズＬ１から構成されている。後側レンズ群ＧＲは正の屈折力を有し、正の屈折力のレンズＬ２と、正の屈折力のレンズＬ３と負の屈折力のレンズＬ４を順次接合してなる正の屈折力の接合レンズから構成されている。 That is, in the perspective objective optical system of the present embodiment, the front lens group GF is disposed on the object side of the prism P, and the rear lens group GR is disposed on the image side of the prism P. The front lens group GF has a negative refractive power and includes a lens L1 having a negative refractive power. The rear lens group GR has a positive refractive power, and has a positive refractive power formed by sequentially joining a lens L2 having a positive refractive power, a lens L3 having a positive refractive power, and a lens L4 having a negative refractive power. It consists of a lens.
　平行平板として描かれたプリズムＰを１回反射型のプリズムとして構成すれば、図６（ａ）に示すように、９０度側方観察が可能な側方視用対物光学系を構成することができる。また、プリズムの反射面を４５度以外の角度に設定にすれば、４５度以外の前方視や後方視などの対物光学系が構成できる。また、２回反射型のプリズムとして構成すれば、４５度の前方視用対物光学系を構成することもできる。 If the prism P drawn as a parallel plate is configured as a single reflection type prism, as shown in FIG. 6A, a side-view objective optical system capable of 90-degree side observation can be configured. it can. Further, if the reflecting surface of the prism is set to an angle other than 45 degrees, an objective optical system such as a front view and a rear view other than 45 degrees can be configured. Further, if it is configured as a twice-reflection type prism, a 45 ° forward-view objective optical system can also be configured.
　更に、プリズムＰは、複数のプリズムによって構成することも可能である。図６（ｂ）には、２つのプリズムで側方視ができる構成が示され、図６（ｃ）には、２つのプリズムで前方視ができる構成が示されている。 Furthermore, the prism P can be composed of a plurality of prisms. FIG. 6B illustrates a configuration in which the two prisms can be viewed from the side, and FIG. 6C illustrates a configuration in which the two prisms can be viewed from the front.
　また、プリズムＰの硝材には、屈折率が１．８以上の高屈折率硝材を用いることが好ましい。このようにすることで、プリズムでの空気換算長を短くすることができる。 Further, it is preferable to use a high refractive index glass material having a refractive index of 1.8 or more for the glass material of the prism P. By doing in this way, the air conversion length in a prism can be shortened.
　負レンズＬ１の硝材をサファイアとしても良い。サファイアは硬度が非常に高い材料なので、外部からの衝撃に強い。よって、物体側のレンズ面に傷が付きにくい。サファイアを用いることで、画像への傷の映り込みや、傷によるフレア発生が起こりにくくなる。なお、負レンズの硝材は、サファイアに限られない。負レンズＬ１に高硬度の結晶材料を用いれば、レンズの表面に傷が付きにくくなる。 The glass material of the negative lens L1 may be sapphire. Since sapphire is a very hard material, it is resistant to external impacts. Therefore, the lens surface on the object side is hardly damaged. By using sapphire, reflection of scratches on an image and occurrence of flare due to scratches are less likely to occur. Note that the glass material of the negative lens is not limited to sapphire. If a crystal material with high hardness is used for the negative lens L1, the surface of the lens is hardly damaged.
　本実施例の斜視対物光学系では、２つの正レンズが用いられている。どちらの正レンズも、両凸形状を有している。低分散硝材では屈折率が低くなるために、低分散硝材を正レンズに用いると、レンズ面の曲率半径が小さくなってしまう。そのため、レンズのコバ厚を十分に確保できなくという問題や、有効口径に対して余裕を持ったレンズ外径を確保できなくなるという問題が生じやすい。そこで、レンズの加工性を考慮すると、正レンズの曲率半径が小さくなり過ぎないようにすることが好ましい。このようなことから、屈折率が１．７以上の高屈折率硝材を、正レンズＬ２と正レンズＬ３の少なくとも一方に用いると良い。 In the perspective objective optical system of this example, two positive lenses are used. Both positive lenses have a biconvex shape. Since the refractive index of a low dispersion glass material is low, if the low dispersion glass material is used for a positive lens, the radius of curvature of the lens surface becomes small. Therefore, the problem that the edge thickness of the lens cannot be sufficiently secured and the problem that the lens outer diameter having a margin with respect to the effective aperture cannot be secured are likely to occur. Therefore, in consideration of the processability of the lens, it is preferable that the radius of curvature of the positive lens is not too small. For this reason, a high refractive index glass material having a refractive index of 1.7 or higher is preferably used for at least one of the positive lens L2 and the positive lens L3.
　正レンズＬ２を両凸レンズで構成する場合、物体側面と像側面は、曲率半径の絶対値が等しい面（以下、「等Ｒ面」という）にすることが好ましい。このようにすると、レンズの前後の判別が不要なため組立てがし易い。 When the positive lens L2 is composed of a biconvex lens, it is preferable that the object side surface and the image side surface are surfaces having the same absolute value of the radius of curvature (hereinafter referred to as “equal R surface”). In this way, it is easy to assemble because there is no need to determine the front and back of the lens.
　正レンズＬ２を両凸レンズで構成する場合、物体側面の曲率半径の絶対値を、像側面の曲率半径の絶対値よりも大きくしても良い。このようにすると、収差補正が容易に行える。 When the positive lens L2 is composed of a biconvex lens, the absolute value of the curvature radius of the object side surface may be larger than the absolute value of the curvature radius of the image side surface. In this way, aberration correction can be easily performed.
　また、撮像素子の画素ピッチが小さくなってくると、これに対応して色収差も小さく抑える必要がある。これに対応するために、接合レンズを構成する負レンズＬ４には、屈折率が１．９以上で、アッベ数が２５以下の高分散硝材を用いることが好ましい。このようにすることで、色収差の補正を良好にすることができる。 Also, as the pixel pitch of the image sensor becomes smaller, it is necessary to suppress chromatic aberration accordingly. In order to cope with this, it is preferable to use a high dispersion glass material having a refractive index of 1.9 or more and an Abbe number of 25 or less for the negative lens L4 constituting the cemented lens. By doing so, the correction of chromatic aberration can be improved.
　一方、接合レンズを構成する正レンズＬ３には、なるべくアッベ数の大きい低分散の硝材を用いるのが良い。例えば、アッベ数５０以上の硝材を、正レンズＬ３に用いることが好ましい。 On the other hand, a low dispersion glass material having a large Abbe number is preferably used for the positive lens L3 constituting the cemented lens. For example, it is preferable to use a glass material having an Abbe number of 50 or more for the positive lens L3.
　また、接合レンズを像面に近い位置に配置することで、接合レンズを通過する光線高が高くなる。光線高が高い位置に接合レンズが位置することで、倍率色収差を良好に補正することができる。このように、接合レンズを像面に近い位置に配置することは、特に倍率色収差の補正に有効である。 Also, by arranging the cemented lens at a position close to the image plane, the height of the light beam passing through the cemented lens becomes high. Since the cemented lens is positioned at a position where the light beam height is high, the lateral chromatic aberration can be favorably corrected. Thus, disposing the cemented lens at a position close to the image plane is particularly effective for correcting lateral chromatic aberration.
　また、本実施例の斜視対物光学系に設けられたプリズム以外の平行平板は、例えば、赤外線カットフィルタや、色温度変換フィルタである。これらのフィルタは、ＣＣＤなどの撮像素子の感度補正に用いられる。 Further, the parallel plate other than the prism provided in the perspective objective optical system of the present embodiment is, for example, an infrared cut filter or a color temperature conversion filter. These filters are used for sensitivity correction of an image sensor such as a CCD.
　また、レーザーカットフィルタや特殊機能フィルタを、斜視対物光学系に配置してもよい。レーザーカットフィルタとしては、例えば、ＹＡＧレーザや半導体レーザ等のレーザ光をカットするためのフィルタがある。特殊機能フィルタとしては、例えば、特定波長域の光線をカットするノッチフィルタがある。 Further, a laser cut filter or a special function filter may be arranged in the perspective objective optical system. Examples of the laser cut filter include a filter for cutting laser light such as a YAG laser and a semiconductor laser. As the special function filter, for example, there is a notch filter that cuts light in a specific wavelength range.
　また、光学フィルタには、吸収型のフィルタ、反射型のフィルタ、もしくはそれらの複合型を用いても良い。また、光学フィルタの表面には反射防止膜が施されていてもよい。 Further, as the optical filter, an absorption type filter, a reflection type filter, or a composite type thereof may be used. Further, an antireflection film may be provided on the surface of the optical filter.
　更に、プリズムの透過面に、赤外線カット特性またはレーザ光カット特性を有する干渉膜を設けることも可能である。 Furthermore, an interference film having infrared cut characteristics or laser light cut characteristics can be provided on the transmission surface of the prism.
　また、本実施例の斜視対物光学系の像面側に配置している平行平板フィルタは、撮像素子に用いるガラスリッドとカバーガラスである。カバーガラスの側面と表面を枠部材で保持することで、撮像素子が枠部材内に固定される。 Further, the parallel plate filter disposed on the image plane side of the perspective objective optical system of the present embodiment is a glass lid and a cover glass used for the image sensor. The image sensor is fixed in the frame member by holding the side surface and the surface of the cover glass with the frame member.
　更に、負レンズＬ１に近接してフィルタＦ１を設けることで、負レンズＬ１の像面側に形成される空気層の体積を小さくすることができる。その結果、レンズ面の結露による曇りの影響を低減することができる。 Furthermore, by providing the filter F1 close to the negative lens L1, the volume of the air layer formed on the image plane side of the negative lens L1 can be reduced. As a result, the influence of fogging due to condensation on the lens surface can be reduced.
　更に、負レンズＬ１とフィルタＦ１とを接合しても良く、また、両者をはんだ等で気密封止しても良い。このようにすることで、より効果的に曇りの発生を防止することができる。 Furthermore, the negative lens L1 and the filter F1 may be joined, and both may be hermetically sealed with solder or the like. By doing in this way, generation | occurrence | production of cloudiness can be prevented more effectively.
　また、本実施例の斜視対物光学系のレンズ枚数は４枚と少ないが、結像性能は良好である。このように、少ないレンズ枚数で対物光学系を構成できるので、コストの低減ができる。 Further, although the number of lenses of the perspective objective optical system of this embodiment is as small as four, the imaging performance is good. In this way, since the objective optical system can be configured with a small number of lenses, the cost can be reduced.
　更に、本実施例の斜視対物光学系では、従来の斜視対物光学系と比べて、空気間隔が狭くなっているので、光学系全体が小型になっている。 Furthermore, in the perspective objective optical system of the present embodiment, the air interval is narrower than that of the conventional perspective objective optical system, so the entire optical system is small.
　以下、実施例について説明する。各収差図において、横軸は収差量を表している。球面収差、非点収差及び倍率収差については、収差量の単位はｍｍである。また、歪曲収差については、収差量の単位は％である。また、ＩＨは像高で単位はｍｍ、ＦＮＯはＦナンバーである。また、収差曲線の波長の単位はｎｍである。 Hereinafter, examples will be described. In each aberration diagram, the horizontal axis represents the amount of aberration. For spherical aberration, astigmatism, and magnification aberration, the unit of aberration is mm. For distortion, the unit of aberration is%. IH is the image height, the unit is mm, and FNO is the F number. The unit of the wavelength of the aberration curve is nm.
（実施例１）
　実施例１に係る斜視対物光学系について説明する。図７は、実施例１に係る斜視対物光学系の断面構成を示す図と収差図であって、（ａ）はレンズ断面、（ｂ）は球面収差（ＳＡ）、（ｃ）は非点収差（ＡＳ）、（ｄ）は歪曲収差（ＤＴ）、（ｅ）は倍率色収差（ＣＣ）を示す。 (Example 1)
A perspective objective optical system according to Example 1 will be described. 7A and 7B are diagrams and aberration diagrams showing the cross-sectional configuration of the perspective objective optical system according to Example 1. FIG. 7A is a lens cross section, FIG. 7B is spherical aberration (SA), and FIG. (AS) and (d) show distortion aberration (DT), and (e) shows lateral chromatic aberration (CC).
　実施例１の斜視対物光学系は、図７（ａ）に示すように、物体側から順に、負屈折力の前側レンズ群ＧＦと、光路変換素子Ｐと、明るさ絞りＳと、正屈折力の後側レンズ群ＧＲと、からなる。 As shown in FIG. 7A, the oblique objective optical system according to the first embodiment includes, in order from the object side, a front lens group GF having a negative refractive power, an optical path conversion element P, an aperture stop S, and a positive refractive power. Rear lens group GR.
　前側レンズ群ＧＦは、物体側が平面である平凹負レンズＬ１からなる。また、前側レンズ群ＧＦには、フィルタＦ１が配置されている。フィルタＦ１は、平凹負レンズＬ１と光路変換素子Ｐとの間に配置されている。 The front lens group GF includes a plano-concave negative lens L1 having a flat object side. A filter F1 is disposed in the front lens group GF. The filter F1 is disposed between the plano-concave negative lens L1 and the optical path conversion element P.
　光路変換素子Ｐは、前側レンズ群ＧＦと後側レンズ群ＧＲの間に配置されている。光路変換素子Ｐはプリズムである。プリズムには屈折率が１．８以上の高屈折率硝材が用いられている。 The optical path conversion element P is disposed between the front lens group GF and the rear lens group GR. The optical path conversion element P is a prism. A high refractive index glass material having a refractive index of 1.8 or more is used for the prism.
　明るさ絞りＳは、光路変換素子Ｐと後側レンズ群ＧＲとの間に配置されている。より具体的には、明るさ絞りＳは、光路変換素子Ｐの像側面に設けられている。 The brightness stop S is disposed between the optical path conversion element P and the rear lens group GR. More specifically, the aperture stop S is provided on the image side surface of the optical path conversion element P.
　後側レンズ群ＧＲは、両凸正レンズＬ２と、両凸正レンズＬ３と、像側に凸面を向けた負メニスカスレンズＬ４と、からなる。ここで、両凸正レンズＬ３と負メニスカスレンズＬ４とで、正屈折力の接合レンズを形成している。両凸正レンズＬ２の両面は、等Ｒ面になっている。後側レンズ群ＧＲには、フィルタＦ２、ガラスリッドＧＬ及びカバーガラスＣＧが配置されている。フィルタＦ２は、両凸正レンズＬ２と接合レンズとの間に配置されている。 The rear lens group GR includes a biconvex positive lens L2, a biconvex positive lens L3, and a negative meniscus lens L4 having a convex surface facing the image side. Here, the biconvex positive lens L3 and the negative meniscus lens L4 form a cemented lens having a positive refractive power. Both surfaces of the biconvex positive lens L2 are equal R surfaces. A filter F2, a glass lid GL, and a cover glass CG are disposed in the rear lens group GR. The filter F2 is disposed between the biconvex positive lens L2 and the cemented lens.
（実施例２）
　実施例２に係る斜視対物光学系について説明する。図８は、実施例２に係る斜視対物光学系の断面構成を示す図と収差図であって、（ａ）はレンズ断面、（ｂ）は球面収差（ＳＡ）、（ｃ）は非点収差（ＡＳ）、（ｄ）は歪曲収差（ＤＴ）、（ｅ）は倍率色収差（ＣＣ）を示す。 (Example 2)
A perspective objective optical system according to Example 2 will be described. FIG. 8 is a diagram showing a cross-sectional configuration of the perspective objective optical system according to Example 2 and aberration diagrams, where (a) is a lens cross section, (b) is spherical aberration (SA), and (c) is astigmatism. (AS) and (d) show distortion aberration (DT), and (e) shows lateral chromatic aberration (CC).
　実施例２の斜視対物光学系は、図８（ａ）に示すように、物体側から順に、負屈折力の前側レンズ群ＧＦと、光路変換素子Ｐと、明るさ絞りＳと、正屈折力の後側レンズ群ＧＲと、からなる。 As shown in FIG. 8A, the perspective objective optical system of Example 2 includes, in order from the object side, a front lens group GF having a negative refractive power, an optical path conversion element P, an aperture stop S, and a positive refractive power. Rear lens group GR.
　前側レンズ群ＧＦは、物体側が平面である平凹負レンズＬ１からなる。また、前側レンズ群ＧＦには、フィルタＦ１が配置されている。フィルタＦ１は、平凹負レンズＬ１と光路変換素子Ｐとの間に配置されている。 The front lens group GF includes a plano-concave negative lens L1 having a flat object side. A filter F1 is disposed in the front lens group GF. The filter F1 is disposed between the plano-concave negative lens L1 and the optical path conversion element P.
　光路変換素子Ｐは、前側レンズ群ＧＦと後側レンズ群ＧＲの間に配置されている。光路変換素子Ｐはプリズムである。プリズムには屈折率が１．８以上の高屈折率硝材が用いられている。 The optical path conversion element P is disposed between the front lens group GF and the rear lens group GR. The optical path conversion element P is a prism. A high refractive index glass material having a refractive index of 1.8 or more is used for the prism.
　明るさ絞りＳは、光路変換素子Ｐと後側レンズ群ＧＲとの間に配置されている。より具体的には、明るさ絞りＳは、光路変換素子Ｐの像側面に設けられている。 The brightness stop S is disposed between the optical path conversion element P and the rear lens group GR. More specifically, the aperture stop S is provided on the image side surface of the optical path conversion element P.
　後側レンズ群ＧＲは、両凸正レンズＬ２と、両凸正レンズＬ３と、像側に凸面を向けた負メニスカスレンズＬ４と、からなる。ここで、両凸正レンズＬ３と負メニスカスレンズＬ４とで、正屈折力の接合レンズを形成している。両凸正レンズＬ２の物体側面の曲率半径の絶対値は、像側面の曲率半径の絶対値よりも大きい。後側レンズ群ＧＲには、フィルタＦ２、ガラスリッドＧＬ及びカバーガラスＣＧが配置されている。フィルタＦ２は、両凸正レンズＬ２と接合レンズとの間に配置されている。 The rear lens group GR includes a biconvex positive lens L2, a biconvex positive lens L3, and a negative meniscus lens L4 having a convex surface facing the image side. Here, the biconvex positive lens L3 and the negative meniscus lens L4 form a cemented lens having a positive refractive power. The absolute value of the radius of curvature of the object side surface of the biconvex positive lens L2 is larger than the absolute value of the radius of curvature of the image side surface. A filter F2, a glass lid GL, and a cover glass CG are disposed in the rear lens group GR. The filter F2 is disposed between the biconvex positive lens L2 and the cemented lens.
（実施例３）
　実施例３に係る斜視対物光学系について説明する。図９は、実施例３に係る斜視対物光学系の断面構成を示す図と収差図であって、（ａ）はレンズ断面、（ｂ）は球面収差（ＳＡ）、（ｃ）は非点収差（ＡＳ）、（ｄ）は歪曲収差（ＤＴ）、（ｅ）は倍率色収差（ＣＣ）を示す。 (Example 3)
A perspective objective optical system according to Example 3 will be described. FIG. 9 is a diagram illustrating a cross-sectional configuration of the perspective objective optical system according to Example 3 and aberration diagrams, where (a) is a lens cross section, (b) is spherical aberration (SA), and (c) is astigmatism. (AS) and (d) show distortion aberration (DT), and (e) shows lateral chromatic aberration (CC).
　実施例３の斜視対物光学系は、図９（ａ）に示すように、物体側から順に、負屈折力の前側レンズ群ＧＦと、光路変換素子Ｐと、明るさ絞りＳと、正屈折力の後側レンズ群ＧＲと、からなる。 As shown in FIG. 9A, the perspective objective optical system according to the third embodiment includes, in order from the object side, a front lens group GF having a negative refractive power, an optical path conversion element P, an aperture stop S, and a positive refractive power. Rear lens group GR.
　前側レンズ群ＧＦは、物体側が平面である平凹負レンズＬ１からなる。また、前側レンズ群ＧＦには、フィルタＦ１が配置されている。フィルタＦ１は、平凹負レンズＬ１と光路変換素子Ｐとの間に配置されている。 The front lens group GF includes a plano-concave negative lens L1 having a flat object side. A filter F1 is disposed in the front lens group GF. The filter F1 is disposed between the plano-concave negative lens L1 and the optical path conversion element P.
　光路変換素子Ｐは、前側レンズ群ＧＦと後側レンズ群ＧＲの間に配置されている。光路変換素子Ｐはプリズムである。プリズムには屈折率が１．８以上の高屈折率硝材が用いられている。 The optical path conversion element P is disposed between the front lens group GF and the rear lens group GR. The optical path conversion element P is a prism. A high refractive index glass material having a refractive index of 1.8 or more is used for the prism.
　明るさ絞りＳは、光路変換素子Ｐと後側レンズ群ＧＲとの間に配置されている。より具体的には、明るさ絞りＳは、光路変換素子Ｐの像側面に設けられている。 The brightness stop S is disposed between the optical path conversion element P and the rear lens group GR. More specifically, the aperture stop S is provided on the image side surface of the optical path conversion element P.
　後側レンズ群ＧＲは、両凸正レンズＬ２と、両凸正レンズＬ３と、像側に凸面を向けた負メニスカスレンズＬ４と、からなる。ここで、両凸正レンズＬ３と負メニスカスレンズＬ４とで、正屈折力の接合レンズを形成している。両凸正レンズＬ２の両面は、等Ｒ面になっている。後側レンズ群ＧＲには、フィルタＦ２、ガラスリッドＧＬ及びカバーガラスＣＧが配置されている。フィルタＦ２は、両凸正レンズＬ２と接合レンズとの間に配置されている。 The rear lens group GR includes a biconvex positive lens L2, a biconvex positive lens L3, and a negative meniscus lens L4 having a convex surface facing the image side. Here, the biconvex positive lens L3 and the negative meniscus lens L4 form a cemented lens having a positive refractive power. Both surfaces of the biconvex positive lens L2 are equal R surfaces. A filter F2, a glass lid GL, and a cover glass CG are disposed in the rear lens group GR. The filter F2 is disposed between the biconvex positive lens L2 and the cemented lens.
（実施例４）
　実施例４に係る斜視対物光学系について説明する。図１０は、実施例４に係る斜視対物光学系の断面構成を示す図と収差図であって、（ａ）はレンズ断面、（ｂ）は球面収差（ＳＡ）、（ｃ）は非点収差（ＡＳ）、（ｄ）は歪曲収差（ＤＴ）、（ｅ）は倍率色収差（ＣＣ）を示す。 Example 4
A perspective objective optical system according to Example 4 will be described. 10A and 10B are a diagram illustrating a cross-sectional configuration of the perspective objective optical system according to Example 4 and aberration diagrams, in which FIG. 10A is a lens cross section, FIG. 10B is spherical aberration (SA), and FIG. (AS) and (d) show distortion aberration (DT), and (e) shows lateral chromatic aberration (CC).
　実施例４の斜視対物光学系は、図１０（ａ）に示すように、物体側から順に、負屈折力の前側レンズ群ＧＦと、光路変換素子Ｐと、明るさ絞りＳと、正屈折力の後側レンズ群ＧＲと、からなる。 As shown in FIG. 10A, the perspective objective optical system of Example 4 includes, in order from the object side, a front lens group GF having a negative refractive power, an optical path conversion element P, an aperture stop S, and a positive refractive power. Rear lens group GR.
　前側レンズ群ＧＦは、物体側が平面である平凹負レンズＬ１からなる。また、前側レンズ群ＧＦには、フィルタＦ１が配置されている。フィルタＦ１は、平凹負レンズＬ１と光路変換素子Ｐとの間に配置されている。 The front lens group GF includes a plano-concave negative lens L1 having a flat object side. A filter F1 is disposed in the front lens group GF. The filter F1 is disposed between the plano-concave negative lens L1 and the optical path conversion element P.
　光路変換素子Ｐは、前側レンズ群ＧＦと後側レンズ群ＧＲの間に配置されている。光路変換素子Ｐはプリズムである。プリズムには屈折率が１．８以上の高屈折率硝材が用いられている。 The optical path conversion element P is disposed between the front lens group GF and the rear lens group GR. The optical path conversion element P is a prism. A high refractive index glass material having a refractive index of 1.8 or more is used for the prism.
　明るさ絞りＳは、光路変換素子Ｐと後側レンズ群ＧＲとの間に配置されている。より具体的には、明るさ絞りＳは、光路変換素子Ｐの像側面に設けられている。 The brightness stop S is disposed between the optical path conversion element P and the rear lens group GR. More specifically, the aperture stop S is provided on the image side surface of the optical path conversion element P.
　後側レンズ群ＧＲは、両凸正レンズＬ２と、両凸正レンズＬ３と、像側に凸面を向けた負メニスカスレンズＬ４と、からなる。ここで、両凸正レンズＬ３と負メニスカスレンズＬ４とで、正屈折力の接合レンズを形成している。両凸正レンズＬ２の両面は、等Ｒ面になっている。後側レンズ群ＧＲには、フィルタＦ２、ガラスリッドＧＬ及びカバーガラスＣＧが配置されている。フィルタＦ２は、両凸正レンズＬ２と接合レンズとの間に配置されている。 The rear lens group GR includes a biconvex positive lens L2, a biconvex positive lens L3, and a negative meniscus lens L4 having a convex surface facing the image side. Here, the biconvex positive lens L3 and the negative meniscus lens L4 form a cemented lens having a positive refractive power. Both surfaces of the biconvex positive lens L2 are equal R surfaces. A filter F2, a glass lid GL, and a cover glass CG are disposed in the rear lens group GR. The filter F2 is disposed between the biconvex positive lens L2 and the cemented lens.
（実施例５）
　実施例５に係る斜視対物光学系について説明する。図１１は、実施例５に係る斜視対物光学系の断面構成を示す図と収差図であって、（ａ）はレンズ断面、（ｂ）は球面収差（ＳＡ）、（ｃ）は非点収差（ＡＳ）、（ｄ）は歪曲収差（ＤＴ）、（ｅ）は倍率色収差（ＣＣ）を示す。 (Example 5)
A perspective objective optical system according to Example 5 will be described. FIG. 11 is a diagram illustrating a cross-sectional configuration of the perspective objective optical system according to Example 5 and aberration diagrams, where (a) is a lens cross section, (b) is spherical aberration (SA), and (c) is astigmatism. (AS) and (d) show distortion aberration (DT), and (e) shows lateral chromatic aberration (CC).
　実施例５の斜視対物光学系は、図１１（ａ）に示すように、物体側から順に、負屈折力の前側レンズ群ＧＦと、光路変換素子Ｐと、明るさ絞りＳと、正屈折力の後側レンズ群ＧＲと、からなる。 As shown in FIG. 11A, the oblique objective optical system of Example 5 includes, in order from the object side, a front lens group GF having a negative refractive power, an optical path conversion element P, an aperture stop S, and a positive refractive power. Rear lens group GR.
　前側レンズ群ＧＦは、物体側が平面である平凹負レンズＬ１からなる。また、前側レンズ群ＧＦには、フィルタＦ１が配置されている。フィルタＦ１は、平凹負レンズＬ１と光路変換素子Ｐとの間に配置されている。 The front lens group GF includes a plano-concave negative lens L1 having a flat object side. A filter F1 is disposed in the front lens group GF. The filter F1 is disposed between the plano-concave negative lens L1 and the optical path conversion element P.
　光路変換素子Ｐは、前側レンズ群ＧＦと後側レンズ群ＧＲの間に配置されている。光路変換素子Ｐはプリズムである。プリズムには屈折率が１．８以上の高屈折率硝材が用いられている。 The optical path conversion element P is disposed between the front lens group GF and the rear lens group GR. The optical path conversion element P is a prism. A high refractive index glass material having a refractive index of 1.8 or more is used for the prism.
　明るさ絞りＳは、光路変換素子Ｐと後側レンズ群ＧＲとの間に配置されている。より具体的には、明るさ絞りＳは、光路変換素子Ｐの像側面に設けられている。 The brightness stop S is disposed between the optical path conversion element P and the rear lens group GR. More specifically, the aperture stop S is provided on the image side surface of the optical path conversion element P.
　後側レンズ群ＧＲは、両凸正レンズＬ２と、両凸正レンズＬ３と、像側に凸面を向けた負メニスカスレンズＬ４と、からなる。ここで、両凸正レンズＬ３と負メニスカスレンズＬ４とで、正屈折力の接合レンズを形成している。両凸正レンズＬ２の両面は、等Ｒ面になっている。後側レンズ群ＧＲには、フィルタＦ２、ガラスリッドＧＬ及びカバーガラスＣＧが配置されている。フィルタＦ２は、両凸正レンズＬ２と接合レンズとの間に配置されている。 The rear lens group GR includes a biconvex positive lens L2, a biconvex positive lens L3, and a negative meniscus lens L4 having a convex surface facing the image side. Here, the biconvex positive lens L3 and the negative meniscus lens L4 form a cemented lens having a positive refractive power. Both surfaces of the biconvex positive lens L2 are equal R surfaces. A filter F2, a glass lid GL, and a cover glass CG are disposed in the rear lens group GR. The filter F2 is disposed between the biconvex positive lens L2 and the cemented lens.
（実施例６）
　実施例６に係る斜視対物光学系について説明する。図１２は、実施例６に係る斜視対物光学系の断面構成を示す図と収差図であって、（ａ）はレンズ断面、（ｂ）は球面収差（ＳＡ）、（ｃ）は非点収差（ＡＳ）、（ｄ）は歪曲収差（ＤＴ）、（ｅ）は倍率色収差（ＣＣ）を示す。 (Example 6)
A perspective objective optical system according to Example 6 will be described. FIG. 12 is a diagram showing a cross-sectional configuration of a perspective objective optical system according to Example 6 and aberration diagrams, where (a) is a lens cross section, (b) is spherical aberration (SA), and (c) is astigmatism. (AS) and (d) show distortion aberration (DT), and (e) shows lateral chromatic aberration (CC).
　実施例６の斜視対物光学系は、図１２（ａ）に示すように、物体側から順に、負屈折力の前側レンズ群ＧＦと、光路変換素子Ｐと、明るさ絞りＳと、正屈折力の後側レンズ群ＧＲと、からなる。 As shown in FIG. 12A, the oblique objective optical system of Example 6 includes, in order from the object side, a front lens group GF having a negative refractive power, an optical path conversion element P, an aperture stop S, and a positive refractive power. Rear lens group GR.
　前側レンズ群ＧＦは、物体側が平面である平凹負レンズＬ１からなる。また、前側レンズ群ＧＦには、フィルタＦ１が配置されている。フィルタＦ１は、平凹負レンズＬ１と光路変換素子Ｐとの間に配置されている。 The front lens group GF includes a plano-concave negative lens L1 having a flat object side. A filter F1 is disposed in the front lens group GF. The filter F1 is disposed between the plano-concave negative lens L1 and the optical path conversion element P.
　光路変換素子Ｐは、前側レンズ群ＧＦと後側レンズ群ＧＲの間に配置されている。光路変換素子Ｐはプリズムである。プリズムには屈折率が１．８以上の高屈折率硝材が用いられている。 The optical path conversion element P is disposed between the front lens group GF and the rear lens group GR. The optical path conversion element P is a prism. A high refractive index glass material having a refractive index of 1.8 or more is used for the prism.
　明るさ絞りＳは、光路変換素子Ｐと後側レンズ群ＧＲとの間に配置されている。より具体的には、明るさ絞りＳは、光路変換素子Ｐの像側面に設けられている。 The brightness stop S is disposed between the optical path conversion element P and the rear lens group GR. More specifically, the aperture stop S is provided on the image side surface of the optical path conversion element P.
　後側レンズ群ＧＲは、両凸正レンズＬ２と、両凸正レンズＬ３と、像側に凸面を向けた負メニスカスレンズＬ４と、からなる。ここで、両凸正レンズＬ３と負メニスカスレンズＬ４とで、正屈折力の接合レンズを形成している。両凸正レンズＬ２の両面は、等Ｒ面になっている。後側レンズ群ＧＲには、フィルタＦ２、ガラスリッドＧＬ及びカバーガラスＣＧが配置されている。フィルタＦ２は、両凸正レンズＬ２と接合レンズとの間に配置されている。 The rear lens group GR includes a biconvex positive lens L2, a biconvex positive lens L3, and a negative meniscus lens L4 having a convex surface facing the image side. Here, the biconvex positive lens L3 and the negative meniscus lens L4 form a cemented lens having a positive refractive power. Both surfaces of the biconvex positive lens L2 are equal R surfaces. A filter F2, a glass lid GL, and a cover glass CG are disposed in the rear lens group GR. The filter F2 is disposed between the biconvex positive lens L2 and the cemented lens.
（実施例７）
　実施例７に係る斜視対物光学系について説明する。図１３は、実施例７に係る斜視対物光学系の断面構成を示す図と収差図であって、（ａ）はレンズ断面、（ｂ）は球面収差（ＳＡ）、（ｃ）は非点収差（ＡＳ）、（ｄ）は歪曲収差（ＤＴ）、（ｅ）は倍率色収差（ＣＣ）を示す。 (Example 7)
A perspective objective optical system according to Example 7 will be described. FIG. 13 is a diagram showing a cross-sectional configuration of a perspective objective optical system according to Example 7 and aberration diagrams, where (a) is a lens cross section, (b) is spherical aberration (SA), and (c) is astigmatism. (AS) and (d) show distortion aberration (DT), and (e) shows lateral chromatic aberration (CC).
　実施例７の斜視対物光学系は、図１３（ａ）に示すように、物体側から順に、負屈折力の前側レンズ群ＧＦと、光路変換素子Ｐと、明るさ絞りＳと、正屈折力の後側レンズ群ＧＲと、からなる。 As shown in FIG. 13A, the perspective objective optical system of Example 7 includes, in order from the object side, a front lens group GF having a negative refractive power, an optical path conversion element P, an aperture stop S, and a positive refractive power. Rear lens group GR.
　前側レンズ群ＧＦは、物体側が平面である平凹負レンズＬ１からなる。また、前側レンズ群ＧＦには、フィルタＦ１が配置されている。フィルタＦ１は、平凹負レンズＬ１と光路変換素子Ｐとの間に配置されている。 The front lens group GF includes a plano-concave negative lens L1 having a flat object side. A filter F1 is disposed in the front lens group GF. The filter F1 is disposed between the plano-concave negative lens L1 and the optical path conversion element P.
　光路変換素子Ｐは、前側レンズ群ＧＦと後側レンズ群ＧＲの間に配置されている。光路変換素子Ｐはプリズムである。プリズムには屈折率が１．８以上の高屈折率硝材が用いられている。 The optical path conversion element P is disposed between the front lens group GF and the rear lens group GR. The optical path conversion element P is a prism. A high refractive index glass material having a refractive index of 1.8 or more is used for the prism.
　明るさ絞りＳは、光路変換素子Ｐと後側レンズ群ＧＲとの間に配置されている。より具体的には、明るさ絞りＳは、光路変換素子Ｐの像側面に設けられている。 The brightness stop S is disposed between the optical path conversion element P and the rear lens group GR. More specifically, the aperture stop S is provided on the image side surface of the optical path conversion element P.
　後側レンズ群ＧＲは、両凸正レンズＬ２と、両凸正レンズＬ３と、像側に凸面を向けた負メニスカスレンズＬ４と、からなる。ここで、両凸正レンズＬ３と負メニスカスレンズＬ４とで、正屈折力の接合レンズを形成している。両凸正レンズＬ２の両面は、等Ｒ面になっている。後側レンズ群ＧＲには、フィルタＦ２、ガラスリッドＧＬ及びカバーガラスＣＧが配置されている。フィルタＦ２は、両凸正レンズＬ２と接合レンズとの間に配置されている。 The rear lens group GR includes a biconvex positive lens L2, a biconvex positive lens L3, and a negative meniscus lens L4 having a convex surface facing the image side. Here, the biconvex positive lens L3 and the negative meniscus lens L4 form a cemented lens having a positive refractive power. Both surfaces of the biconvex positive lens L2 are equal R surfaces. A filter F2, a glass lid GL, and a cover glass CG are disposed in the rear lens group GR. The filter F2 is disposed between the biconvex positive lens L2 and the cemented lens.
（実施例８）
　実施例８に係る斜視対物光学系について説明する。図１４は、実施例８に係る斜視対物光学系の断面構成を示す図と収差図であって、（ａ）はレンズ断面、（ｂ）は球面収差（ＳＡ）、（ｃ）は非点収差（ＡＳ）、（ｄ）は歪曲収差（ＤＴ）、（ｅ）は倍率色収差（ＣＣ）を示す。 (Example 8)
A perspective objective optical system according to Example 8 will be described. FIG. 14 is a diagram showing a cross-sectional configuration of the perspective objective optical system according to Example 8 and aberration diagrams, where (a) is a lens cross section, (b) is spherical aberration (SA), and (c) is astigmatism. (AS) and (d) show distortion aberration (DT), and (e) shows lateral chromatic aberration (CC).
　実施例８の斜視対物光学系は、図１４（ａ）に示すように、物体側から順に、負屈折力の前側レンズ群ＧＦと、光路変換素子Ｐと、明るさ絞りＳと、正屈折力の後側レンズ群ＧＲと、からなる。 As shown in FIG. 14A, the perspective objective optical system according to the eighth embodiment includes, in order from the object side, a front lens group GF having a negative refractive power, an optical path conversion element P, an aperture stop S, and a positive refractive power. Rear lens group GR.
　前側レンズ群ＧＦは、物体側が平面である平凹負レンズＬ１からなる。平凹負レンズＬ１にはサファイアが用いられている。また、前側レンズ群ＧＦには、フィルタＦ１が配置されている。フィルタＦ１は、平凹負レンズＬ１と光路変換素子Ｐとの間に配置されている。 The front lens group GF includes a plano-concave negative lens L1 having a flat object side. Sapphire is used for the planoconcave negative lens L1. A filter F1 is disposed in the front lens group GF. The filter F1 is disposed between the plano-concave negative lens L1 and the optical path conversion element P.
　光路変換素子Ｐは、前側レンズ群ＧＦと後側レンズ群ＧＲの間に配置されている。光路変換素子Ｐはプリズムである。プリズムには屈折率が１．８以上の高屈折率硝材が用いられている。 The optical path conversion element P is disposed between the front lens group GF and the rear lens group GR. The optical path conversion element P is a prism. A high refractive index glass material having a refractive index of 1.8 or more is used for the prism.
　明るさ絞りＳは、光路変換素子Ｐと後側レンズ群ＧＲとの間に配置されている。より具体的には、明るさ絞りＳは、光路変換素子Ｐの像側面に設けられている。 The brightness stop S is disposed between the optical path conversion element P and the rear lens group GR. More specifically, the aperture stop S is provided on the image side surface of the optical path conversion element P.
　後側レンズ群ＧＲは、両凸正レンズＬ２と、両凸正レンズＬ３と、像側に凸面を向けた負メニスカスレンズＬ４と、からなる。ここで、両凸正レンズＬ３と負メニスカスレンズＬ４とで、正屈折力の接合レンズを形成している。両凸正レンズＬ２の物体側面の曲率半径の絶対値は、像側面の曲率半径の絶対値よりも大きい。後側レンズ群ＧＲには、フィルタＦ２、ガラスリッドＧＬ及びカバーガラスＣＧが配置されている。フィルタＦ２は、両凸正レンズＬ２と接合レンズとの間に配置されている。 The rear lens group GR includes a biconvex positive lens L2, a biconvex positive lens L3, and a negative meniscus lens L4 having a convex surface facing the image side. Here, the biconvex positive lens L3 and the negative meniscus lens L4 form a cemented lens having a positive refractive power. The absolute value of the radius of curvature of the object side surface of the biconvex positive lens L2 is larger than the absolute value of the radius of curvature of the image side surface. A filter F2, a glass lid GL, and a cover glass CG are disposed in the rear lens group GR. The filter F2 is disposed between the biconvex positive lens L2 and the cemented lens.
（実施例９）
　実施例９に係る斜視対物光学系について説明する。図１５は、実施例９に係る斜視対物光学系の断面構成を示す図と収差図であって、（ａ）はレンズ断面、（ｂ）は球面収差（ＳＡ）、（ｃ）は非点収差（ＡＳ）、（ｄ）は歪曲収差（ＤＴ）、（ｅ）は倍率色収差（ＣＣ）を示す。 Example 9
A perspective objective optical system according to Example 9 will be described. FIG. 15 is a diagram illustrating a cross-sectional configuration of a perspective objective optical system according to Example 9, and aberration diagrams. FIG. 15A is a lens cross section, FIG. 15B is spherical aberration (SA), and FIG. (AS) and (d) show distortion aberration (DT), and (e) shows lateral chromatic aberration (CC).
　実施例９の斜視対物光学系は、図１５（ａ）に示すように、物体側から順に、負屈折力の前側レンズ群ＧＦと、光路変換素子Ｐと、明るさ絞りＳと、正屈折力の後側レンズ群ＧＲと、からなる。 As shown in FIG. 15A, the perspective objective optical system according to the ninth embodiment has a negative refractive power front lens group GF, an optical path conversion element P, an aperture stop S, and a positive refractive power in order from the object side. Rear lens group GR.
　前側レンズ群ＧＦは、物体側が平面である平凹負レンズＬ１からなる。また、前側レンズ群ＧＦには、フィルタＦ１が配置されている。フィルタＦ１は、平凹負レンズＬ１と光路変換素子Ｐとの間に配置されている。 The front lens group GF includes a plano-concave negative lens L1 having a flat object side. A filter F1 is disposed in the front lens group GF. The filter F1 is disposed between the plano-concave negative lens L1 and the optical path conversion element P.
　光路変換素子Ｐは、前側レンズ群ＧＦと後側レンズ群ＧＲの間に配置されている。光路変換素子Ｐはプリズムである。プリズムには屈折率が１．８以上の高屈折率硝材が用いられている。 The optical path conversion element P is disposed between the front lens group GF and the rear lens group GR. The optical path conversion element P is a prism. A high refractive index glass material having a refractive index of 1.8 or more is used for the prism.
　明るさ絞りＳは、光路変換素子Ｐと後側レンズ群ＧＲとの間に配置されている。より具体的には、明るさ絞りＳは、光路変換素子Ｐの像側面に設けられている。 The brightness stop S is disposed between the optical path conversion element P and the rear lens group GR. More specifically, the aperture stop S is provided on the image side surface of the optical path conversion element P.
　後側レンズ群ＧＲは、両凸正レンズＬ２と、両凸正レンズＬ３と、像側に凸面を向けた負メニスカスレンズＬ４と、からなる。ここで、両凸正レンズＬ３と負メニスカスレンズＬ４とで、正屈折力の接合レンズを形成している。両凸正レンズＬ２の両面は、等Ｒ面になっている。後側レンズ群ＧＲには、ガラスリッドＧＬとカバーガラスＣＧが配置されている。 The rear lens group GR includes a biconvex positive lens L2, a biconvex positive lens L3, and a negative meniscus lens L4 having a convex surface facing the image side. Here, the biconvex positive lens L3 and the negative meniscus lens L4 form a cemented lens having a positive refractive power. Both surfaces of the biconvex positive lens L2 are equal R surfaces. A glass lid GL and a cover glass CG are disposed in the rear lens group GR.
　本実施例に係る斜視対物光学系では、光学フィルタとしての機能はフィルタＦ１に集約されている。よって、斜視対物光学系に配置されている光学フィルタは１枚だけである。 In the perspective objective optical system according to the present embodiment, the function as an optical filter is concentrated in the filter F1. Therefore, only one optical filter is arranged in the perspective objective optical system.
（実施例１０）
　実施例１０に係る斜視対物光学系について説明する。図１６は、実施例１０に係る斜視対物光学系の断面構成を示す図と収差図であって、（ａ）はレンズ断面、（ｂ）は球面収差（ＳＡ）、（ｃ）は非点収差（ＡＳ）、（ｄ）は歪曲収差（ＤＴ）、（ｅ）は倍率色収差（ＣＣ）を示す。 (Example 10)
A perspective objective optical system according to Example 10 will be described. FIG. 16 is a diagram showing a cross-sectional configuration of a perspective objective optical system according to Example 10 and aberration diagrams, where (a) is a lens cross section, (b) is spherical aberration (SA), and (c) is astigmatism. (AS) and (d) show distortion aberration (DT), and (e) shows lateral chromatic aberration (CC).
　実施例１０の斜視対物光学系は、図１６（ａ）に示すように、物体側から順に、負屈折力の前側レンズ群ＧＦと、光路変換素子Ｐと、明るさ絞りＳと、正屈折力の後側レンズ群ＧＲと、からなる。 As shown in FIG. 16A, the oblique objective optical system of Example 10 includes, in order from the object side, a front lens unit GF having a negative refractive power, an optical path conversion element P, an aperture stop S, and a positive refractive power. Rear lens group GR.
　前側レンズ群ＧＦは、物体側が平面である平凹負レンズＬ１からなる。また、前側レンズ群ＧＦには、フィルタＦ１が配置されている。フィルタＦ１は、平凹負レンズＬ１と光路変換素子Ｐとの間に配置されている。 The front lens group GF includes a plano-concave negative lens L1 having a flat object side. A filter F1 is disposed in the front lens group GF. The filter F1 is disposed between the plano-concave negative lens L1 and the optical path conversion element P.
　光路変換素子Ｐは、前側レンズ群ＧＦと後側レンズ群ＧＲの間に配置されている。光路変換素子Ｐはプリズムである。プリズムには屈折率が１．８以上の高屈折率硝材が用いられている。 The optical path conversion element P is disposed between the front lens group GF and the rear lens group GR. The optical path conversion element P is a prism. A high refractive index glass material having a refractive index of 1.8 or more is used for the prism.
　明るさ絞りＳは、光路変換素子Ｐと後側レンズ群ＧＲとの間に配置されている。より具体的には、明るさ絞りＳは、光路変換素子Ｐの像側面に設けられている。 The brightness stop S is disposed between the optical path conversion element P and the rear lens group GR. More specifically, the aperture stop S is provided on the image side surface of the optical path conversion element P.
　後側レンズ群ＧＲは、両凸正レンズＬ２と、両凸正レンズＬ３と、像側に凸面を向けた負メニスカスレンズＬ４と、からなる。ここで、両凸正レンズＬ３と負メニスカスレンズＬ４とで、正屈折力の接合レンズを形成している。両凸正レンズＬ２の両面は、等Ｒ面になっている。後側レンズ群ＧＲには、フィルタＦ２、ガラスリッドＧＬ及びカバーガラスＣＧが配置されている。フィルタＦ２は、両凸正レンズＬ２と接合レンズとの間に配置されている。 The rear lens group GR includes a biconvex positive lens L2, a biconvex positive lens L3, and a negative meniscus lens L4 having a convex surface facing the image side. Here, the biconvex positive lens L3 and the negative meniscus lens L4 form a cemented lens having a positive refractive power. Both surfaces of the biconvex positive lens L2 are equal R surfaces. A filter F2, a glass lid GL, and a cover glass CG are disposed in the rear lens group GR. The filter F2 is disposed between the biconvex positive lens L2 and the cemented lens.
（実施例１１）
　実施例１１に係る斜視対物光学系について説明する。図１７は、実施例１１に係る斜視対物光学系の断面構成を示す図と収差図であって、（ａ）はレンズ断面、（ｂ）は球面収差（ＳＡ）、（ｃ）は非点収差（ＡＳ）、（ｄ）は歪曲収差（ＤＴ）、（ｅ）は倍率色収差（ＣＣ）を示す。 (Example 11)
A perspective objective optical system according to Example 11 will be described. FIG. 17 is a diagram showing a cross-sectional configuration of a perspective objective optical system according to Example 11 and aberration diagrams, where (a) is a lens cross section, (b) is spherical aberration (SA), and (c) is astigmatism. (AS) and (d) show distortion aberration (DT), and (e) shows lateral chromatic aberration (CC).
　実施例１１の斜視対物光学系は、図１７（ａ）に示すように、物体側から順に、負屈折力の前側レンズ群ＧＦと、光路変換素子Ｐと、明るさ絞りＳと、正屈折力の後側レンズ群ＧＲと、からなる。 As shown in FIG. 17A, the oblique objective optical system of Example 11 has a negative refractive power front lens group GF, an optical path conversion element P, an aperture stop S, and a positive refractive power in order from the object side. Rear lens group GR.
　前側レンズ群ＧＦは、物体側が平面である平凹負レンズＬ１からなる。また、前側レンズ群ＧＦには、フィルタＦ１が配置されている。フィルタＦ１は、平凹負レンズＬ１と光路変換素子Ｐとの間に配置されている。 The front lens group GF includes a plano-concave negative lens L1 having a flat object side. A filter F1 is disposed in the front lens group GF. The filter F1 is disposed between the plano-concave negative lens L1 and the optical path conversion element P.
　光路変換素子Ｐは、前側レンズ群ＧＦと後側レンズ群ＧＲの間に配置されている。光路変換素子Ｐはプリズムである。プリズムには屈折率が１．８以上の高屈折率硝材が用いられている。 The optical path conversion element P is disposed between the front lens group GF and the rear lens group GR. The optical path conversion element P is a prism. A high refractive index glass material having a refractive index of 1.8 or more is used for the prism.
　明るさ絞りＳは、光路変換素子Ｐと後側レンズ群ＧＲとの間に配置されている。より具体的には、明るさ絞りＳは、光路変換素子Ｐの像側面に設けられている。 The brightness stop S is disposed between the optical path conversion element P and the rear lens group GR. More specifically, the aperture stop S is provided on the image side surface of the optical path conversion element P.
　後側レンズ群ＧＲは、両凸正レンズＬ２と、両凸正レンズＬ３と、像側に凸面を向けた負メニスカスレンズＬ４と、からなる。ここで、両凸正レンズＬ３と負メニスカスレンズＬ４とで、正屈折力の接合レンズを形成している。両凸正レンズＬ２の物体側面の曲率半径の絶対値は、像側面の曲率半径の絶対値よりも大きい。後側レンズ群ＧＲには、フィルタＦ２、ガラスリッドＧＬ及びカバーガラスＣＧが配置されている。フィルタＦ２は、両凸正レンズＬ２と接合レンズとの間に配置されている。 The rear lens group GR includes a biconvex positive lens L2, a biconvex positive lens L3, and a negative meniscus lens L4 having a convex surface facing the image side. Here, the biconvex positive lens L3 and the negative meniscus lens L4 form a cemented lens having a positive refractive power. The absolute value of the radius of curvature of the object side surface of the biconvex positive lens L2 is larger than the absolute value of the radius of curvature of the image side surface. A filter F2, a glass lid GL, and a cover glass CG are disposed in the rear lens group GR. The filter F2 is disposed between the biconvex positive lens L2 and the cemented lens.
（実施例１２）
　実施例１２に係る斜視対物光学系について説明する。図１８は、実施例１２に係る斜視対物光学系の断面構成を示す図と収差図であって、（ａ）はレンズ断面、（ｂ）は球面収差（ＳＡ）、（ｃ）は非点収差（ＡＳ）、（ｄ）は歪曲収差（ＤＴ）、（ｅ）は倍率色収差（ＣＣ）を示す。 Example 12
A perspective objective optical system according to Example 12 will be described. FIG. 18 is a diagram showing a cross-sectional configuration of a perspective objective optical system according to Example 12 and aberration diagrams, where (a) is a lens cross section, (b) is spherical aberration (SA), and (c) is astigmatism. (AS) and (d) show distortion aberration (DT), and (e) shows lateral chromatic aberration (CC).
　実施例１２の斜視対物光学系は、図１８（ａ）に示すように、物体側から順に、負屈折力の前側レンズ群ＧＦと、光路変換素子Ｐと、明るさ絞りＳと、正屈折力の後側レンズ群ＧＲと、からなる。 As shown in FIG. 18A, the squint objective optical system of the twelfth embodiment has, in order from the object side, a front lens group GF having a negative refractive power, an optical path conversion element P, an aperture stop S, and a positive refractive power. Rear lens group GR.
　前側レンズ群ＧＦは、物体側が平面である平凹負レンズＬ１からなる。また、前側レンズ群ＧＦには、フィルタＦ１が配置されている。フィルタＦ１は、平凹負レンズＬ１と光路変換素子Ｐとの間に配置されている。 The front lens group GF includes a plano-concave negative lens L1 having a flat object side. A filter F1 is disposed in the front lens group GF. The filter F1 is disposed between the plano-concave negative lens L1 and the optical path conversion element P.
　光路変換素子Ｐは、前側レンズ群ＧＦと後側レンズ群ＧＲの間に配置されている。光路変換素子Ｐはプリズムである。プリズムには屈折率が１．８以上の高屈折率硝材が用いられている。 The optical path conversion element P is disposed between the front lens group GF and the rear lens group GR. The optical path conversion element P is a prism. A high refractive index glass material having a refractive index of 1.8 or more is used for the prism.
　明るさ絞りＳは、光路変換素子Ｐと後側レンズ群ＧＲとの間に配置されている。より具体的には、明るさ絞りＳは、光路変換素子Ｐの像側面に設けられている。 The brightness stop S is disposed between the optical path conversion element P and the rear lens group GR. More specifically, the aperture stop S is provided on the image side surface of the optical path conversion element P.
　後側レンズ群ＧＲは、両凸正レンズＬ２と、両凸正レンズＬ３と、像側に凸面を向けた負メニスカスレンズＬ４と、からなる。ここで、両凸正レンズＬ３と負メニスカスレンズＬ４とで、正屈折力の接合レンズを形成している。両凸正レンズＬ２の物体側面の曲率半径の絶対値は、像側面の曲率半径の絶対値よりも大きい。後側レンズ群ＧＲには、フィルタＦ２、ガラスリッドＧＬ及びカバーガラスＣＧが配置されている。フィルタＦ２は、両凸正レンズＬ２と接合レンズとの間に配置されている。 The rear lens group GR includes a biconvex positive lens L2, a biconvex positive lens L3, and a negative meniscus lens L4 having a convex surface facing the image side. Here, the biconvex positive lens L3 and the negative meniscus lens L4 form a cemented lens having a positive refractive power. The absolute value of the radius of curvature of the object side surface of the biconvex positive lens L2 is larger than the absolute value of the radius of curvature of the image side surface. A filter F2, a glass lid GL, and a cover glass CG are disposed in the rear lens group GR. The filter F2 is disposed between the biconvex positive lens L2 and the cemented lens.
（実施例１３）
　実施例１３に係る斜視対物光学系について説明する。図１９は、実施例１３に係る斜視対物光学系の断面構成を示す図と収差図であって、（ａ）はレンズ断面、（ｂ）は球面収差（ＳＡ）、（ｃ）は非点収差（ＡＳ）、（ｄ）は歪曲収差（ＤＴ）、（ｅ）は倍率色収差（ＣＣ）を示す。 (Example 13)
A perspective objective optical system according to Example 13 will be described. FIG. 19 is a diagram illustrating a cross-sectional configuration of a perspective objective optical system according to Example 13 and aberration diagrams, where (a) is a lens cross section, (b) is spherical aberration (SA), and (c) is astigmatism. (AS) and (d) show distortion aberration (DT), and (e) shows lateral chromatic aberration (CC).
　実施例１３の斜視対物光学系は、図１９（ａ）に示すように、物体側から順に、負屈折力の前側レンズ群ＧＦと、光路変換素子Ｐと、明るさ絞りＳと、正屈折力の後側レンズ群ＧＲと、からなる。 As shown in FIG. 19A, the oblique objective optical system according to the thirteenth embodiment includes, in order from the object side, a front lens group GF having a negative refractive power, an optical path conversion element P, an aperture stop S, and a positive refractive power. Rear lens group GR.
　前側レンズ群ＧＦは、物体側が平面である平凹負レンズＬ１からなる。また、前側レンズ群ＧＦには、フィルタＦ１が配置されている。フィルタＦ１は、平凹負レンズＬ１と光路変換素子Ｐとの間に配置されている。 The front lens group GF includes a plano-concave negative lens L1 having a flat object side. A filter F1 is disposed in the front lens group GF. The filter F1 is disposed between the plano-concave negative lens L1 and the optical path conversion element P.
　光路変換素子Ｐは、前側レンズ群ＧＦと後側レンズ群ＧＲの間に配置されている。光路変換素子Ｐはプリズムである。プリズムには屈折率が１．８以上の高屈折率硝材が用いられている。 The optical path conversion element P is disposed between the front lens group GF and the rear lens group GR. The optical path conversion element P is a prism. A high refractive index glass material having a refractive index of 1.8 or more is used for the prism.
　明るさ絞りＳは、光路変換素子Ｐと後側レンズ群ＧＲとの間に配置されている。より具体的には、明るさ絞りＳは、光路変換素子Ｐの像側面に設けられている。 The brightness stop S is disposed between the optical path conversion element P and the rear lens group GR. More specifically, the aperture stop S is provided on the image side surface of the optical path conversion element P.
　後側レンズ群ＧＲは、両凸正レンズＬ２と、両凸正レンズＬ３と、像側に凸面を向けた負メニスカスレンズＬ４と、からなる。ここで、両凸正レンズＬ３と負メニスカスレンズＬ４とで、正屈折力の接合レンズを形成している。両凸正レンズＬ２の物体側面の曲率半径の絶対値は、像側面の曲率半径の絶対値よりも大きい。後側レンズ群ＧＲには、フィルタＦ２、ガラスリッドＧＬ及びカバーガラスＣＧが配置されている。フィルタＦ２は、両凸正レンズＬ２と接合レンズとの間に配置されている。 The rear lens group GR includes a biconvex positive lens L2, a biconvex positive lens L3, and a negative meniscus lens L4 having a convex surface facing the image side. Here, the biconvex positive lens L3 and the negative meniscus lens L4 form a cemented lens having a positive refractive power. The absolute value of the radius of curvature of the object side surface of the biconvex positive lens L2 is larger than the absolute value of the radius of curvature of the image side surface. A filter F2, a glass lid GL, and a cover glass CG are disposed in the rear lens group GR. The filter F2 is disposed between the biconvex positive lens L2 and the cemented lens.
（実施例１４）
　実施例１４に係る斜視対物光学系について説明する。図２０は、実施例１４に係る斜視対物光学系の断面構成を示す図と収差図であって、（ａ）はレンズ断面、（ｂ）は球面収差（ＳＡ）、（ｃ）は非点収差（ＡＳ）、（ｄ）は歪曲収差（ＤＴ）、（ｅ）は倍率色収差（ＣＣ）を示す。 (Example 14)
A perspective objective optical system according to Example 14 will be described. FIG. 20 is a diagram illustrating a cross-sectional configuration of a perspective objective optical system according to Example 14 and aberration diagrams, where (a) is a lens cross section, (b) is spherical aberration (SA), and (c) is astigmatism. (AS) and (d) show distortion aberration (DT), and (e) shows lateral chromatic aberration (CC).
　実施例１４の斜視対物光学系は、図２０（ａ）に示すように、物体側から順に、負屈折力の前側レンズ群ＧＦと、光路変換素子Ｐと、明るさ絞りＳと、正屈折力の後側レンズ群ＧＲと、からなる。 As shown in FIG. 20A, the oblique objective optical system of the fourteenth embodiment has, in order from the object side, a front lens unit GF having a negative refractive power, an optical path conversion element P, an aperture stop S, and a positive refractive power. Rear lens group GR.
　前側レンズ群ＧＦは、物体側が平面である平凹負レンズＬ１からなる。また、前側レンズ群ＧＦには、フィルタＦ１は、平凹負レンズＬ１と光路変換素子Ｐとの間に配置されている。 The front lens group GF includes a plano-concave negative lens L1 having a flat object side. In the front lens group GF, the filter F1 is disposed between the plano-concave negative lens L1 and the optical path conversion element P.
　光路変換素子Ｐは、前側レンズ群ＧＦと後側レンズ群ＧＲの間に配置されている。光路変換素子Ｐはプリズムである。プリズムには屈折率が１．５程度の低屈折率硝材が用いられている。 The optical path conversion element P is disposed between the front lens group GF and the rear lens group GR. The optical path conversion element P is a prism. A low refractive index glass material having a refractive index of about 1.5 is used for the prism.
　明るさ絞りＳは、光路変換素子Ｐと後側レンズ群ＧＲとの間に配置されている。より具体的には、明るさ絞りＳは、光路変換素子Ｐの像側面に設けられている。 The brightness stop S is disposed between the optical path conversion element P and the rear lens group GR. More specifically, the aperture stop S is provided on the image side surface of the optical path conversion element P.
　後側レンズ群ＧＲは、両凸正レンズＬ２と、両凸正レンズＬ３と、平凹負レンズＬ４と、からなる。ここで、両凸正レンズＬ３と平凹負レンズＬ４とで、正屈折力の接合レンズを形成している。両凸正レンズＬ２の物体側面の曲率半径の絶対値は、像側面の曲率半径の絶対値よりも大きい。後側レンズ群ＧＲには、フィルタＦ２、ガラスリッドＧＬ及びカバーガラスＣＧが配置されている。フィルタＦ２は、両凸正レンズＬ２と接合レンズとの間に配置されている。 The rear lens group GR includes a biconvex positive lens L2, a biconvex positive lens L3, and a planoconcave negative lens L4. Here, the biconvex positive lens L3 and the plano-concave negative lens L4 form a cemented lens having a positive refractive power. The absolute value of the radius of curvature of the object side surface of the biconvex positive lens L2 is larger than the absolute value of the radius of curvature of the image side surface. A filter F2, a glass lid GL, and a cover glass CG are disposed in the rear lens group GR. The filter F2 is disposed between the biconvex positive lens L2 and the cemented lens.
　本実施例に係る斜視対物光学系では、プリズムに低屈折率硝材が用いられている。そのため、前側レンズ群ＧＦと後側レンズ群ＧＲとの間隔（空気換算長）を広くして、プリズムが配置できるようにする必要がある。ただし、低屈折率硝材は、高屈折率硝材よりも低分散である。そのため、接合レンズにアッベ数が２０未満の高屈折率で異常分散な硝材を用いなくても、色収差の補正が可能である。本実施例では、平凹負レンズＬ４に、屈折率が１．８程度、アッベ数が２２程度の硝材を使用している。 In the perspective objective optical system according to the present embodiment, a low refractive index glass material is used for the prism. Therefore, it is necessary to increase the distance (air conversion length) between the front lens group GF and the rear lens group GR so that the prism can be arranged. However, the low refractive index glass material has lower dispersion than the high refractive index glass material. Therefore, it is possible to correct chromatic aberration without using a high refractive index and abnormally dispersed glass material having an Abbe number of less than 20 for the cemented lens. In the present embodiment, a glass material having a refractive index of about 1.8 and an Abbe number of about 22 is used for the plano-concave negative lens L4.
　また、光路変換素子（プリズム）に低屈折率硝材を使用すると、高屈折率硝材の場合と比べて前側レンズ群と後側レンズ群との間隔が長くなるため、負レンズの外径が大型化しやすくなる。しかしながら、本実施例に係る斜視対物光学系では光路変換素子を短く構成したため、前側レンズ群のレンズ径は他の実施例と同程度の径になっている。 In addition, when a low refractive index glass material is used for the optical path conversion element (prism), the distance between the front lens group and the rear lens group becomes longer than in the case of a high refractive index glass material, so the outer diameter of the negative lens increases. It becomes easy. However, in the perspective objective optical system according to the present embodiment, since the optical path changing element is configured to be short, the lens diameter of the front lens group is the same as that of the other embodiments.
　また、接合レンズの両凸正レンズＬ３と平凹負レンズＬ４の屈折率差は約０．０７と小さい。また、平凹負レンズＬ４の像側面は、平面で構成されている。そのため、レンズの加工性が良く、組立時のレンズの前後の判別もし易い。 Also, the refractive index difference between the biconvex positive lens L3 and the plano-concave negative lens L4 of the cemented lens is as small as about 0.07. The image side surface of the plano-concave negative lens L4 is a flat surface. Therefore, the processability of the lens is good, and it is easy to determine before and after the lens at the time of assembly.
（実施例１５）
　実施例１５に係る斜視対物光学系について説明する。図２１は、実施例１５に係る斜視対物光学系の断面構成を示す図と収差図であって、（ａ）はレンズ断面、（ｂ）は球面収差（ＳＡ）、（ｃ）は非点収差（ＡＳ）、（ｄ）は歪曲収差（ＤＴ）、（ｅ）は倍率色収差（ＣＣ）を示す。 (Example 15)
A perspective objective optical system according to Example 15 will be described. FIG. 21 is a diagram showing a cross-sectional configuration of the perspective objective optical system according to Example 15 and aberration diagrams, where (a) is a lens cross section, (b) is spherical aberration (SA), and (c) is astigmatism. (AS) and (d) show distortion aberration (DT), and (e) shows lateral chromatic aberration (CC).
　実施例１５の斜視対物光学系は、図２１（ａ）に示すように、物体側から順に、負屈折力の前側レンズ群ＧＦと、光路変換素子Ｐと、明るさ絞りＳと、正屈折力の後側レンズ群ＧＲと、からなる。 As shown in FIG. 21A, the perspective objective optical system of Example 15 is arranged in order from the object side, the front lens group GF having a negative refractive power, an optical path conversion element P, an aperture stop S, and a positive refractive power. Rear lens group GR.
　前側レンズ群ＧＦは、物体側が平面である平凹負レンズＬ１からなる。また、前側レンズ群ＧＦには、フィルタＦ１が配置されている。フィルタＦ１は、平凹負レンズＬ１と光路変換素子Ｐとの間に配置されている。 The front lens group GF includes a plano-concave negative lens L1 having a flat object side. A filter F1 is disposed in the front lens group GF. The filter F1 is disposed between the plano-concave negative lens L1 and the optical path conversion element P.
　光路変換素子Ｐは、前側レンズ群ＧＦと後側レンズ群ＧＲの間に配置されている。光路変換素子Ｐはプリズムである。プリズムには屈折率が１．８以上の高屈折率硝材が用いられている。 The optical path conversion element P is disposed between the front lens group GF and the rear lens group GR. The optical path conversion element P is a prism. A high refractive index glass material having a refractive index of 1.8 or more is used for the prism.
　明るさ絞りＳは、光路変換素子Ｐと後側レンズ群ＧＲとの間に配置されている。より具体的には、明るさ絞りＳは、光路変換素子Ｐの像側面に設けられている。 The brightness stop S is disposed between the optical path conversion element P and the rear lens group GR. More specifically, the aperture stop S is provided on the image side surface of the optical path conversion element P.
　後側レンズ群ＧＲは、両凸正レンズＬ２と、両凸正レンズＬ３と、像側に凸面を向けた負メニスカスレンズＬ４と、からなる。ここで、両凸正レンズＬ３と負メニスカスレンズＬ４とで、正屈折力の接合レンズを形成している。両凸正レンズＬ２の物体側面の曲率半径の絶対値は、像側面の曲率半径の絶対値よりも大きい。後側レンズ群ＧＲには、フィルタＦ２、ガラスリッドＧＬ及びカバーガラスＣＧが配置されている。フィルタＦ２は、両凸正レンズＬ２と接合レンズとの間に配置されている。 The rear lens group GR includes a biconvex positive lens L2, a biconvex positive lens L3, and a negative meniscus lens L4 having a convex surface facing the image side. Here, the biconvex positive lens L3 and the negative meniscus lens L4 form a cemented lens having a positive refractive power. The absolute value of the radius of curvature of the object side surface of the biconvex positive lens L2 is larger than the absolute value of the radius of curvature of the image side surface. A filter F2, a glass lid GL, and a cover glass CG are disposed in the rear lens group GR. The filter F2 is disposed between the biconvex positive lens L2 and the cemented lens.
　本実施例に係る斜視対物光学系では、画角を１２０度というように広角化しているが、プリズムに屈折率が１．８以上の高屈折率硝材を用いることで、平凹負レンズＬ１の像側面の曲率半径（絶対値）が小さくならないようにしている。また、Ｆナンバーが３．６程度というように、明るく高性能な斜視対物光学系になっている。 In the perspective objective optical system according to the present embodiment, the angle of view is widened to 120 degrees, but by using a high refractive index glass material having a refractive index of 1.8 or more for the prism, the plano-concave negative lens L1 The curvature radius (absolute value) of the image side surface is not reduced. In addition, it is a bright and high-performance perspective objective optical system with an F number of about 3.6.
　以上説明したように、各実施例の斜視対物光学系は、プリズムの物体側に配置された前側レンズ群と、プリズムの像側に配置された後側レンズ群と、前側レンズ群は負の屈折力を有すると共に、負の屈折力のレンズから構成され、後側レンズ群は正の屈折力を有すると共に、正の屈折力のレンズと正の屈折力を有する接合レンズとから構成され、接合レンズは、正の屈折力のレンズと負の屈折力のレンズを順次接合してなり、開口絞りをプリズムと後群レンズ群との間に具備する。 As described above, the perspective objective optical system of each embodiment includes the front lens group disposed on the object side of the prism, the rear lens group disposed on the image side of the prism, and the front lens group having negative refraction. The rear lens group has a positive refractive power and is composed of a positive refractive power lens and a cemented lens having a positive refractive power. In which a lens having a positive refractive power and a lens having a negative refractive power are sequentially joined, and an aperture stop is provided between the prism and the rear lens group.
　各実施例の斜視対物光学系は、撮像素子の小型化および多画素化に対応して光学性能を向上させた最適なレンズ構成を有し、この構成によって、内視鏡先端部の細径化にも寄与し得る。更に、各実施例の斜視対物光学系は、各条件式を満足しているため、諸収差が良好に補正されている。 The perspective objective optical system of each embodiment has an optimal lens configuration that improves optical performance in response to the downsizing of the image sensor and the increase in the number of pixels, and this configuration reduces the diameter of the distal end portion of the endoscope. Can also contribute. Furthermore, since the perspective objective optical system of each example satisfies each conditional expression, various aberrations are corrected well.
　以下に、上記各実施例の数値データを示す。記号は、ｒは各面の曲率半径、ｄは各光学部材の肉厚または空気間隔、ｎｄは各光学部材のｄ線に対する屈折率、νｄは各光学部材のｄ線に対するアッベ数、ｆは斜視対物光学系の全系の焦点距離、ＩＨは像高、ωは半画角、ｆFは前側レンズ群の焦点距離、ｆRは後側レンズ群の焦点距離、Ｄ１は前側レンズ群の負レンズの像側面から明るさ絞りまでの空気換算長、Ｄ２は後側レンズ群の最終レンズの像側面から像面までの空気換算長、Ｒcは後側レンズ群の接合レンズの接合面の曲率半径、ｆ2は後側レンズ群の正レンズの焦点距離、ｆ3は後側レンズ群の接合レンズの焦点距離、ＴＷは最大像高時の像面への光線入射角度を表している。また、ｒ、ｄ、ＩＨ、空気換算長および各焦点距の単位はｍｍである。また、ｆは１ｍｍに規格化されている。 Below, the numerical data of each said Example are shown. Symbols, r is the radius of curvature of each surface, d is the thickness or air spacing of each optical member, nd is the refractive index of each optical member with respect to the d-line, νd is the Abbe number of each optical member with respect to the d-line, f is a perspective view The focal length of the entire objective optical system, IH is the image height, ω is the half field angle, f F is the focal length of the front lens group, f R is the focal length of the rear lens group, and D1 is the negative lens of the front lens group. the equivalent air length from the image side surface to the aperture stop, the air-equivalent length from the image side surface of the last lens of D2 is the rear lens group to the image plane, R c is a curvature of the cemented surface of the cemented lens in the rear lens group , F 2 represents the focal length of the positive lens in the rear lens group, f 3 represents the focal length of the cemented lens in the rear lens group, and TW represents the light incident angle on the image plane at the maximum image height. The unit of r, d, IH, air conversion length and focal length is mm. F is standardized to 1 mm.
数値実施例１
単位　ｍｍ
 
面データ
  面番号     r         d        nd        νd
    1        ∞      0.5824   1.88300     40.76
    2       1.3715   0.9318
    3        ∞      0.5824   1.51633     64.14
    4        ∞      0.0582
    5        ∞      3.3735   1.88300     40.76
    6        ∞      0
    7(絞り)  ∞      0.1893
    8       3.9034   1.2667   1.75500     52.32
    9      -3.9034   0.0874
   10        ∞      0.8736   1.52100     65.13
   11        ∞      0.1165
   12       2.4271   1.6452   1.58913     61.14
   13      -1.5608   0.4368   1.92286     18.90
   14     -18.2083   0.6471
   15        ∞      0.4805   1.88300     40.76
   16        ∞      0.0146   1.51300     64.00
   17        ∞      0.5824   1.61062     50.49
   18       0
  (像面)
 
各種データ
ＩＨ       0.754
ω        46.963
Ｆｎｏ     5.585 Numerical example 1
Unit mm

Surface data Surface number r d nd νd
1 ∞ 0.5824 1.88300 40.76
2 1.3715 0.9318
3 ∞ 0.5824 1.51633 64.14
4 ∞ 0.0582
5 ∞ 3.3735 1.88300 40.76
6 ∞ 0
7 (Aperture) ∞ 0.1893
8 3.9034 1.2667 1.75500 52.32
9 -3.9034 0.0874
10 ∞ 0.8736 1.52100 65.13
11 ∞ 0.1165
12 2.4271 1.6452 1.58913 61.14
13 -1.5608 0.4368 1.92286 18.90
14 -18.2083 0.6471
15 ∞ 0.4805 1.88300 40.76
16 ∞ 0.0146 1.51300 64.00
17 ∞ 0.5824 1.61062 50.49
18 0
(Image plane)

Various data IH 0.754
ω 46.963
Fno 5.585
数値実施例２
単位　ｍｍ
 
面データ
  面番号     r         d        nd        νd
    1        ∞      0.5849   1.88300     40.76
    2       1.3488   0.9358
    3        ∞      0.5849   1.51633     64.14
    4        ∞      0.0585
    5        ∞      3.3878   1.88300     40.76
    6        ∞      0
    7(絞り)  ∞      0.1901
    8       4.7265   1.1067   1.72916     54.68
    9      -3.3389   0.0731
   10        ∞      0.8773   1.52100     65.13
   11        ∞      0.1024
   12       2.5638   1.9281   1.58913     61.14
   13      -1.6295   0.4533   1.92286     18.90
   14     -17.7766   0.5258
   15        ∞      0.4825   1.51633     64.14
   16        ∞      0.0146   1.51300     64.00
   17        ∞      0.5849   1.61062     50.49
   18       0
  (像面)
 
各種データ
ＩＨ       0.757
ω        47.49
Ｆｎｏ     5.337 Numerical example 2
Unit mm

Surface data Surface number r d nd νd
1 ∞ 0.5849 1.88300 40.76
2 1.3488 0.9358
3 ∞ 0.5849 1.51633 64.14
4 ∞ 0.0585
5 ∞ 3.3878 1.88300 40.76
6 ∞ 0
7 (Aperture) ∞ 0.1901
8 4.7265 1.1067 1.72916 54.68
9 -3.3389 0.0731
10 ∞ 0.8773 1.52100 65.13
11 ∞ 0.1024
12 2.5638 1.9281 1.58913 61.14
13 -1.6295 0.4533 1.92286 18.90
14 -17.7766 0.5258
15 ∞ 0.4825 1.51633 64.14
16 ∞ 0.0146 1.51300 64.00
17 ∞ 0.5849 1.61062 50.49
18 0
(Image plane)

Various data IH 0.757
ω 47.49
Fno 5.337
数値実施例３
単位　ｍｍ
 
面データ
  面番号     r         d        nd        νd
    1        ∞      0.5774   1.88300     40.76
    2       1.2959   0.9238
    3        ∞      0.5774   1.51633     64.14
    4        ∞      0.0577
    5        ∞      3.3446   1.88300     40.76
    6        ∞      0
    7(絞り)  ∞      0.1877
    8       4.2060   1.2820   1.77250     49.60
    9      -4.2060   0.0866
   10        ∞      0.8661   1.52100     65.13
   11        ∞      0.1155
   12       2.2312   1.6570   1.58913     61.14
   13      -1.4930   0.4330   1.92286     18.90
   14     -25.0484   0.6461
   15        ∞      0.5774   1.51633     64.14
   16        ∞      0.0144   1.51300     64.00
   17        ∞      0.5774   1.61062     50.49
   18       0
  (像面)
 
各種データ
ＩＨ       0.748
ω        46.852
Ｆｎｏ     5.382 Numerical Example 3
Unit mm

Surface data Surface number r d nd νd
1 ∞ 0.5774 1.88300 40.76
2 1.2959 0.9238
3 ∞ 0.5774 1.51633 64.14
4 ∞ 0.0577
5 ∞ 3.3446 1.88300 40.76
6 ∞ 0
7 (Aperture) ∞ 0.1877
8 4.2060 1.2820 1.77250 49.60
9 -4.2060 0.0866
10 ∞ 0.8661 1.52100 65.13
11 ∞ 0.1155
12 2.2312 1.6570 1.58913 61.14
13 -1.4930 0.4330 1.92286 18.90
14 -25.0484 0.6461
15 ∞ 0.5774 1.51633 64.14
16 ∞ 0.0144 1.51300 64.00
17 ∞ 0.5774 1.61062 50.49
18 0
(Image plane)

Various data IH 0.748
ω 46.852
Fno 5.382
数値実施例４
単位　ｍｍ
 
面データ
  面番号     r         d        nd        νd
    1        ∞      0.5574   1.88300     40.76
    2       1.4786   0.8083
    3        ∞      0.5574   1.51633     64.14
    4        ∞      0.0557
    5        ∞      3.2290   1.88300     40.76
    6        ∞      0
    7(絞り)  ∞      0.2508
    8       3.4826   1.3936   1.72916     54.68
    9      -3.4826   0.1394
   10        ∞      0.4320   1.51401     75.26
   11        ∞      0.1394
   12       2.6785   1.2542   1.51633     64.15
   13      -1.6389   0.3763   1.92286     18.90
   14      -4.6881   0.7878
   15        ∞      0.5574   1.51633     64.14
   16        ∞      0.0139   1.51300     53.00
   17        ∞      0.5574   1.50510     63.26
   18       0
  (像面)
 
各種データ
ＩＨ       0.715
ω        44.041
Ｆｎｏ     3.582 Numerical Example 4
Unit mm

Surface data Surface number r d nd νd
1 ∞ 0.5574 1.88300 40.76
2 1.4786 0.8083
3 ∞ 0.5574 1.51633 64.14
4 ∞ 0.0557
5 ∞ 3.2290 1.88300 40.76
6 ∞ 0
7 (Aperture) ∞ 0.2508
8 3.4826 1.3936 1.72916 54.68
9 -3.4826 0.1394
10 ∞ 0.4320 1.51401 75.26
11 ∞ 0.1394
12 2.6785 1.2542 1.51633 64.15
13 -1.6389 0.3763 1.92286 18.90
14 -4.6881 0.7878
15 ∞ 0.5574 1.51633 64.14
16 ∞ 0.0139 1.51300 53.00
17 ∞ 0.5574 1.50510 63.26
18 0
(Image plane)

Various data IH 0.715
ω 44.041
Fno 3.582
数値実施例５
単位　ｍｍ
 
面データ 
  面番号     r         d        nd        νd
    1        ∞    0.5574   1.88300     40.76
    2     1.4786   0.8083
    3        ∞    0.5574   1.51633     64.14
    4        ∞    0.0557     
    5        ∞    3.2290   1.88300     40.76
    6        ∞    0
    7(絞り)  ∞    0.2508
    8     3.4826   1.3936   1.72916     54.68
    9    -3.4826   0.1394
   10        ∞    0.4320   1.51401     75.26
   11        ∞    0.1394
   12     2.6785   1.2542   1.51633     64.15
   13    -1.6389   0.3763   1.92286     18.90
   14    -4.6881   0.7921
   15        ∞    0.5574   1.51633     64.14
   16        ∞    0.0139   1.50808     63.26
   17        ∞    0.5574   1.52275     55.29
   18       0
  (像面)
 
各種データ
ＩＨ       0.739
ω        45.823
Ｆｎｏ     3.582 Numerical Example 5
Unit mm

Surface data
Surface number r d nd νd
1 ∞ 0.5574 1.88300 40.76
2 1.4786 0.8083
3 ∞ 0.5574 1.51633 64.14
4 ∞ 0.0557
5 ∞ 3.2290 1.88300 40.76
6 ∞ 0
7 (Aperture) ∞ 0.2508
8 3.4826 1.3936 1.72916 54.68
9 -3.4826 0.1394
10 ∞ 0.4320 1.51401 75.26
11 ∞ 0.1394
12 2.6785 1.2542 1.51633 64.15
13 -1.6389 0.3763 1.92286 18.90
14 -4.6881 0.7921
15 ∞ 0.5574 1.51633 64.14
16 ∞ 0.0139 1.50808 63.26
17 ∞ 0.5574 1.52275 55.29
18 0
(Image plane)

Various data IH 0.739
ω 45.823
Fno 3.582
数値実施例６
単位　ｍｍ
 
面データ
  面番号     r         d        nd        νd
    1        ∞      0.6039   1.88300     40.76
    2       1.3977   0.9902
    3        ∞      0.6039   1.51633     64.14
    4        ∞      0.0604
    5        ∞      3.4984   1.88300     40.76
    6        ∞      0
    7(絞り)  ∞      0.2202
    8       4.1101   1.3586   1.75500     52.32
    9      -4.1101   0.0906
   10        ∞      0.9059   1.52100     65.13
   11        ∞      0.1208
   12       2.4546   1.6388   1.58913     61.14
   13      -1.6488   0.4530   1.92286     18.90
   14     -15.7302   0.6285
   15        ∞      0.5285   1.51633     64.14
   16        ∞      0.0151   1.51300     64.00
   17        ∞      0.6039   1.61062     50.49
   18       0
  (像面)
 
各種データ
ＩＨ       0.782
ω        49.682
Ｆｎｏ     3.919 Numerical Example 6
Unit mm

Surface data Surface number r d nd νd
1 ∞ 0.6039 1.88300 40.76
2 1.3977 0.9902
3 ∞ 0.6039 1.51633 64.14
4 ∞ 0.0604
5 ∞ 3.4984 1.88300 40.76
6 ∞ 0
7 (Aperture) ∞ 0.2202
8 4.1101 1.3586 1.75500 52.32
9 -4.1101 0.0906
10 ∞ 0.9059 1.52100 65.13
11 ∞ 0.1208
12 2.4546 1.6388 1.58913 61.14
13 -1.6488 0.4530 1.92286 18.90
14 -15.7302 0.6285
15 ∞ 0.5285 1.51633 64.14
16 ∞ 0.0151 1.51300 64.00
17 ∞ 0.6039 1.61062 50.49
18 0
(Image plane)

Various data IH 0.782
ω 49.682
Fno 3.919
数値実施例７
単位　ｍｍ
 
面データ
  面番号     r         d        nd        νd
    1        ∞      0.6047   1.88300     40.76
    2       1.4045   0.9860
    3        ∞      0.6047   1.51633     64.14
    4        ∞      0.0605
    5        ∞      3.5027   1.80610     40.92
    6        ∞      0
    7(絞り)  ∞      0.2150
    8       4.1478   1.3511   1.75500     52.32
    9      -4.1478   0.0907
   10        ∞      0.9070   1.52100     65.13
   11        ∞      0.1209
   12       2.4738   1.6527   1.58913     61.14
   13      -1.6436   0.4535   1.92286     18.90
   14     -16.3751   0.6376
   15        ∞      0.5291   1.51633     64.14
   16        ∞      0.0151   1.51300     64.00
   17        ∞      0.6047   1.61062     50.49
   18       0
  (像面)
 
各種データ
ＩＨ       0.783
ω        49.783
Ｆｎｏ     3.963 Numerical Example 7
Unit mm

Surface data Surface number r d nd νd
1 ∞ 0.6047 1.88300 40.76
2 1.4045 0.9860
3 ∞ 0.6047 1.51633 64.14
4 ∞ 0.0605
5 ∞ 3.5027 1.80610 40.92
6 ∞ 0
7 (Aperture) ∞ 0.2150
8 4.1478 1.3511 1.75500 52.32
9 -4.1478 0.0907
10 ∞ 0.9070 1.52100 65.13
11 ∞ 0.1209
12 2.4738 1.6527 1.58913 61.14
13 -1.6436 0.4535 1.92286 18.90
14 -16.3751 0.6376
15 ∞ 0.5291 1.51633 64.14
16 ∞ 0.0151 1.51300 64.00
17 ∞ 0.6047 1.61062 50.49
18 0
(Image plane)

Various data IH 0.783
ω 49.783
Fno 3.963
数値実施例８
単位　ｍｍ
 
面データ
  面番号     r         d        nd        νd
    1        ∞      0.6025   1.76820     71.79
    2       1.2469   0.9706
    3        ∞      0.6025   1.51633     64.14
    4        ∞      0.0603
    5        ∞      3.4902   1.80610     40.92
    6        ∞      0
    7(絞り)  ∞      0.2007
    8       4.3747   0.8191   1.75500     52.32
    9      -3.9694   0.0904
   10        ∞      0.9038   1.52100     65.13
   11        ∞      0.1205
   12       2.3851   1.6115   1.58913     61.14
   13      -1.6658   0.4519   1.92286     18.90
   14     -17.1437   0.6244
   15        ∞      0.5272   1.51633     64.14
   16        ∞      0.0151   1.51300     64.00
   17        ∞      0.6025   1.61062     50.49
   18       0
  (像面)
 
各種データ
ＩＨ       0.78
ω        49.868
Ｆｎｏ     3.914 Numerical Example 8
Unit mm

Surface data Surface number r d nd νd
1 ∞ 0.6025 1.76820 71.79
2 1.2469 0.9706
3 ∞ 0.6025 1.51633 64.14
4 ∞ 0.0603
5 ∞ 3.4902 1.80610 40.92
6 ∞ 0
7 (Aperture) ∞ 0.2007
8 4.3747 0.8191 1.75500 52.32
9 -3.9694 0.0904
10 ∞ 0.9038 1.52100 65.13
11 ∞ 0.1205
12 2.3851 1.6115 1.58913 61.14
13 -1.6658 0.4519 1.92286 18.90
14 -17.1437 0.6244
15 ∞ 0.5272 1.51633 64.14
16 ∞ 0.0151 1.51300 64.00
17 ∞ 0.6025 1.61062 50.49
18 0
(Image plane)

Various data IH 0.78
ω 49.868
Fno 3.914
数値実施例９
単位　ｍｍ
 
面データ
  面番号     r         d        nd        νd
    1        ∞      0.6063   1.88300     40.76
    2       1.4043   0.7963
    3        ∞      0.9094   1.52100     65.13
    4        ∞      0.0606
    5        ∞      3.5118   1.88300     40.76
    6        ∞      0
    7(絞り)  ∞      0.2215
    8       4.1211   1.3238   1.75500     52.32
    9      -4.1211   0.8039
   10       2.4518   1.6393   1.58913     61.14
   11      -1.6490   0.4547   1.92286     18.90
   12     -15.6642   0.6244
   13        ∞      0.5305   1.51633     64.14
   14        ∞      0.0152   1.51300     64.00
   15        ∞      0.6063   1.61062     50.49
   16       0
  (像面)
 
各種データ
ＩＨ       0.785
ω        49.819
Ｆｎｏ     3.902 Numerical Example 9
Unit mm

Surface data Surface number r d nd νd
1 ∞ 0.6063 1.88300 40.76
2 1.4043 0.7963
3 ∞ 0.9094 1.52100 65.13
4 ∞ 0.0606
5 ∞ 3.5118 1.88300 40.76
6 ∞ 0
7 (Aperture) ∞ 0.2215
8 4.1211 1.3238 1.75500 52.32
9 -4.1211 0.8039
10 2.4518 1.6393 1.58913 61.14
11 -1.6490 0.4547 1.92286 18.90
12 -15.6642 0.6244
13 ∞ 0.5305 1.51633 64.14
14 ∞ 0.0152 1.51300 64.00
15 ∞ 0.6063 1.61062 50.49
16 0
(Image plane)

Various data IH 0.785
ω 49.819
Fno 3.902
数値実施例１０
単位　ｍｍ
 
面データ
  面番号     r         d        nd        νd
    1        ∞      0.7091   1.88300     40.76
    2       1.5748   1.2402
    3        ∞      0.7091   1.51633     64.14
    4        ∞      0.0709
    5        ∞      4.1075   1.88300     40.76
    6        ∞      0
    7(絞り)  ∞      0.3344
    8       4.7563   1.4638   1.75500     52.32
    9      -4.7563   0.1064
   10        ∞      1.0636   1.52100     65.13
   11        ∞      0.1418
   12       2.6909   1.7969   1.58913     61.14
   13      -2.0324   0.5318   1.92286     18.90
   14     -12.6152   0.6184
   15        ∞      0.6205   1.88300     40.76
   16        ∞      0.0177   1.51300     64.00
   17        ∞      0.7091   1.61062     50.49
   18       0
  (像面)
 
各種データ
ＩＨ       0.775
ω        49.712
Ｆｎｏ     4.826 Numerical Example 10
Unit mm

Surface data Surface number r d nd νd
1 ∞ 0.7091 1.88300 40.76
2 1.5748 1.2402
3 ∞ 0.7091 1.51633 64.14
4 ∞ 0.0709
5 ∞ 4.1075 1.88300 40.76
6 ∞ 0
7 (Aperture) ∞ 0.3344
8 4.7563 1.4638 1.75500 52.32
9 -4.7563 0.1064
10 ∞ 1.0636 1.52100 65.13
11 ∞ 0.1418
12 2.6909 1.7969 1.58913 61.14
13 -2.0324 0.5318 1.92286 18.90
14 -12.6152 0.6184
15 ∞ 0.6205 1.88300 40.76
16 ∞ 0.0177 1.51300 64.00
17 ∞ 0.7091 1.61062 50.49
18 0
(Image plane)

Various data IH 0.775
ω 49.712
Fno 4.826
数値実施例１１
単位　ｍｍ
 
面データ
  面番号     r         d        nd        νd
    1        ∞      0.7151   1.88300     40.76
    2       1.6305   1.2317
    3        ∞      0.7151   1.51633     64.14
    4        ∞      0.0715
    5        ∞      4.1421   1.88300     40.76
    6        ∞      0
    7(絞り)  ∞      0.2647
    8       5.3567   1.0020   1.75500     52.32
    9      -4.4586   0.1073
   10        ∞      1.0726   1.52100     65.13
   11        ∞      0.1430
   12       3.4196   1.9581   1.72916     54.68
   13      -1.6984   0.5363   1.92286     18.90
   14     -15.0024   0.6204
   15        ∞      0.6257   1.88300     40.76
   16        ∞      0.0179   1.51300     64.00
   17        ∞      0.7151   1.61062     50.49
   18       0
  (像面)
 
各種データ
ＩＨ       0.781
ω        49.83
Ｆｎｏ     4.686 Numerical Example 11
Unit mm

Surface data Surface number r d nd νd
1 ∞ 0.7151 1.88300 40.76
2 1.6305 1.2317
3 ∞ 0.7151 1.51633 64.14
4 ∞ 0.0715
5 ∞ 4.1421 1.88300 40.76
6 ∞ 0
7 (Aperture) ∞ 0.2647
8 5.3567 1.0020 1.75500 52.32
9 -4.4586 0.1073
10 ∞ 1.0726 1.52100 65.13
11 ∞ 0.1430
12 3.4196 1.9581 1.72916 54.68
13 -1.6984 0.5363 1.92286 18.90
14 -15.0024 0.6204
15 ∞ 0.6257 1.88300 40.76
16 ∞ 0.0179 1.51300 64.00
17 ∞ 0.7151 1.61062 50.49
18 0
(Image plane)

Various data IH 0.781
ω 49.83
Fno 4.686
数値実施例１２
単位　ｍｍ
 
面データ
  面番号     r         d        nd        νd
    1        ∞      0.7148   1.88300     40.76
    2       1.6360   1.2338
    3        ∞      0.7148   1.51633     64.14
    4        ∞      0.0715
    5        ∞      4.1406   1.88300     40.76
    6        ∞      0
    7(絞り)  ∞      0.2616
    8       5.7330   0.9374   1.78590     44.20
    9      -4.5891   0.1072
   10        ∞      1.0722   1.52100     65.13
   11        ∞      0.1430
   12       3.3805   1.9484   1.72916     54.68
   13      -1.6935   0.5361   1.92286     18.90
   14     -14.9347   0.6272
   15        ∞      0.6255   1.88300     40.76
   16        ∞      0.0179   1.51300     64.00
   17        ∞      0.7148   1.61062     50.49
   18       0
  (像面)
 
各種データ
ＩＨ       0.781
ω        49.8
Ｆｎｏ     4.679 Numerical example 12
Unit mm

Surface data Surface number r d nd νd
1 ∞ 0.7148 1.88300 40.76
2 1.6360 1.2338
3 ∞ 0.7148 1.51633 64.14
4 ∞ 0.0715
5 ∞ 4.1406 1.88300 40.76
6 ∞ 0
7 (Aperture) ∞ 0.2616
8 5.7330 0.9374 1.78590 44.20
9 -4.5891 0.1072
10 ∞ 1.0722 1.52100 65.13
11 ∞ 0.1430
12 3.3805 1.9484 1.72916 54.68
13 -1.6935 0.5361 1.92286 18.90
14 -14.9347 0.6272
15 ∞ 0.6255 1.88300 40.76
16 ∞ 0.0179 1.51300 64.00
17 ∞ 0.7148 1.61062 50.49
18 0
(Image plane)

Various data IH 0.781
ω 49.8
Fno 4.679
数値実施例１３
単位　ｍｍ
 
面データ
  面番号     r         d        nd        νd
    1        ∞      0.5257   1.88300     40.76
    2       1.3088   0.7804
    3        ∞      0.5257   1.51633     64.14
    4        ∞      0.0526
    5        ∞      3.0450   1.80610     40.92
    6        ∞      0
    7(絞り)  ∞      0.0848
    8       3.7410   1.1367   1.75500     52.32
    9      -3.5359   0.0789
   10        ∞      0.7885   1.52100     65.13
   11        ∞      0.1051
   12       2.3989   1.5316   1.58913     61.14
   13      -1.2564   0.4164   1.80810     22.76
   14     -33.5075   0.6417
   15        ∞      0.4600   1.51633     64.14
   16        ∞      0.0131   1.51300     64.00
   17        ∞      0.5257   1.61062     50.49
   18       0
  (像面)
 
各種データ
ＩＨ       0.769
ω        47.829
Ｆｎｏ     4.29 Numerical Example 13
Unit mm

Surface data Surface number r d nd νd
1 ∞ 0.5257 1.88300 40.76
2 1.3088 0.7804
3 ∞ 0.5257 1.51633 64.14
4 ∞ 0.0526
5 ∞ 3.0450 1.80610 40.92
6 ∞ 0
7 (Aperture) ∞ 0.0848
8 3.7410 1.1367 1.75500 52.32
9 -3.5359 0.0789
10 ∞ 0.7885 1.52100 65.13
11 ∞ 0.1051
12 2.3989 1.5316 1.58913 61.14
13 -1.2564 0.4164 1.80810 22.76
14 -33.5075 0.6417
15 ∞ 0.4600 1.51633 64.14
16 ∞ 0.0131 1.51300 64.00
17 ∞ 0.5257 1.61062 50.49
18 0
(Image plane)

Various data IH 0.769
ω 47.829
Fno 4.29
数値実施例１４
単位　ｍｍ
 
面データ
  面番号     r         d        nd        νd
    1        ∞      0.5392   1.88300     40.76
    2       1.4109   0.7483
    3        ∞      0.5392   1.51633     64.14
    4        ∞      0.0539
    5        ∞      3.1230   1.51633     64.14
    6        ∞      0
    7(絞り)  ∞      0.0809
    8       4.7542   1.4154   1.77250     49.60
    9      -3.7982   0.0809
   10        ∞      0.8087   1.52100     65.13
   11        ∞      0.1078
   12       3.4342   1.7847   1.72916     54.68
   13      -1.1903   0.5256   1.80810     22.76
   14        ∞      0.7540
   15        ∞      0.4718   1.51633     64.14
   16        ∞      0.0135   1.51300     64.00
   17        ∞      0.5392   1.61062     50.49
   18       0
  (像面)
 
各種データ
ＩＨ       0.789
ω        49.83
Ｆｎｏ     4.282 Numerical example 14
Unit mm

Surface data Surface number r d nd νd
1 ∞ 0.5392 1.88300 40.76
2 1.4109 0.7483
3 ∞ 0.5392 1.51633 64.14
4 ∞ 0.0539
5 ∞ 3.1230 1.51633 64.14
6 ∞ 0
7 (Aperture) ∞ 0.0809
8 4.7542 1.4154 1.77250 49.60
9 -3.7982 0.0809
10 ∞ 0.8087 1.52100 65.13
11 ∞ 0.1078
12 3.4342 1.7847 1.72916 54.68
13 -1.1903 0.5256 1.80810 22.76
14 ∞ 0.7540
15 ∞ 0.4718 1.51633 64.14
16 ∞ 0.0135 1.51300 64.00
17 ∞ 0.5392 1.61062 50.49
18 0
(Image plane)

Various data IH 0.789
ω 49.83
Fno 4.282
数値実施例１５
単位　ｍｍ
 
面データ
  面番号     r         d        nd        νd
    1        ∞      0.6803   1.88300     40.76
    2       1.5386   1.1825
    3        ∞      0.6803   1.51633     64.14
    4        ∞      0.0680
    5        ∞      3.9405   1.88300     40.76
    6        ∞      0
    7(絞り)  ∞      0.3052
    8       5.2193   1.3688   1.77250     49.60
    9      -4.3467   0.1020
   10        ∞      1.0204   1.52100     65.13
   11        ∞      0.1361
   12       2.5755   1.6909   1.58913     61.14
   13      -2.0613   0.5201   1.95906     17.47
   14     -13.8236   0.6296
   15        ∞      0.5952   1.51633     64.14
   16        ∞      0.0170   1.51300     64.00
   17        ∞      0.6803   1.61062     50.49
   18       0
  (像面)
 
各種データ
ＩＨ       0.881
ω        59.74
Ｆｎｏ     3.569 Numerical example 15
Unit mm

Surface data Surface number r d nd νd
1 ∞ 0.6803 1.88300 40.76
2 1.5386 1.1825
3 ∞ 0.6803 1.51633 64.14
4 ∞ 0.0680
5 ∞ 3.9405 1.88300 40.76
6 ∞ 0
7 (Aperture) ∞ 0.3052
8 5.2193 1.3688 1.77250 49.60
9 -4.3467 0.1020
10 ∞ 1.0204 1.52100 65.13
11 ∞ 0.1361
12 2.5755 1.6909 1.58913 61.14
13 -2.0613 0.5201 1.95906 17.47
14 -13.8236 0.6296
15 ∞ 0.5952 1.51633 64.14
16 ∞ 0.0170 1.51300 64.00
17 ∞ 0.6803 1.61062 50.49
18 0
(Image plane)

Various data IH 0.881
ω 59.74
Fno 3.569
　以下、実施例１～実施例１５に係る対物光学系における条件式（１）～（９）の数値を示す。
           実施例１    実施例２    実施例３    実施例４    実施例５
(1)fF/f      -1.553      -1.528      -1.468      -1.675      -1.675
(2)fR/f       2.062       2.056       2.069       2.108       2.108
(3)|fF/fR|  -0.753      -0.743      -0.709      -0.794      -0.794
(4)D1/f      3.166       3.179       3.139       2.946       2.946
(5)D2/f      1.274       1.217       1.395       1.535       1.535
(6)D1/D2     2.486       2.613       2.25        1.92        1.92
(7)f3/f2      3.008       2.962       2.681       2.55        2.55
(8)|Rc|/f     1.561       1.629       1.493       1.639       1.639
(9)TW       -10.032     -10.411     -10          -7.365      -7.59
 
           実施例６    実施例７    実施例８    実施例９    実施例１０
(1)fF/f      -1.583      -1.591      -1.623      -1.59       -1.783
(2)fR/f       2.163       2.179       2.08        2.16        2.457
(3)|fF/fR|  -0.732      -0.73       -0.78       -0.736      -0.726
(4)D1/f      3.307       3.385       3.361       3.320       3.96
(5)D2/f      1.362       1.372       1.356       1.361       1.4
(6)D1/D2     2.428       2.467       2.478       2.440       2.829
(7)f3/f2      2.612       2.673       2.555       2.601       1.996
(8)|Rc|/f     1.649       1.644       1.666       1.649       2.032
(9)TW        -9.433      -9.563     -10.863      -9.529      -7.277
 
           実施例１１  実施例１２  実施例１３  実施例１４  実施例１５
(1)fF/f      -1.847      -1.853      -1.482      -1.598      -1.742
(2)fR/f       2.395       2.382       1.927       2.159       2.37
(3)|fF/fR|  -0.771      -0.778      -0.769      -0.74       -0.735
(4)D1/f      3.975       3.976       2.866       3.217       3.792
(5)D2/f      1.408       1.415       1.28        1.409       1.456
(6)D1/D2     2.822       2.81        2.239       2.284       2.605
(7)f3/f2      1.733       1.705       2.973       2.115       2.125
(8)|Rc|/f     1.698       1.693       1.256       1.19        2.061
(9)TW        -8.003      -8.17      -11.235      -9.216      -8.876
 
           実施例１    実施例２    実施例３    実施例４    実施例５
f            1           1           1           1           1
fF           -1.553      -1.528      -1.468      -1.675      -1.675
fR            2.062       2.056       2.069       2.108       2.108
D1           3.166       3.179       3.139       2.946       2.946
D2           1.274       1.217       1.395       1.535       1.535
f2            2.779       2.848       2.916       2.608       2.608
f3            8.358       8.438       7.818       6.652       6.652
Rc           -1.561      -1.629      -1.493      -1.639      -1.639
 
           実施例６    実施例７    実施例８    実施例９    実施例１０
f            1           1           1           1           1
fF           -1.583      -1.591      -1.623      -1.59       -1.783
fR            2.163       2.179       2.08        2.16        2.457
D1           3.307       3.385       3.361       3.320       3.96
D2           1.362       1.372       1.356       1.361       1.4
f2            2.93        2.954       2.878       2.932       3.373
f3            7.655       7.896       7.355       7.625       6.734
Rc           -1.649      -1.644      -1.666      -1.649      -2.032
 
           実施例１１  実施例１２  実施例１３  実施例１４  実施例１５
f            1           1           1           1           1
fF           -1.847      -1.853      -1.482      -1.598      -1.742
fR            2.395       2.382       1.927       2.159       2.37
D1           3.975       3.976       2.866       3.217       3.792
D2           1.408       1.415       1.28        1.409       1.456
f2            3.371       3.378       2.581       2.946       3.274
f3            5.841       5.758       7.673       6.229       6.957
Rc           -1.698      -1.693      -1.256      -1.19       -2.061 The numerical values of conditional expressions (1) to (9) in the objective optical systems according to Examples 1 to 15 are shown below.
Example 1 Example 2 Example 3 Example 4 Example 5
(1) f F / f    -1.553 -1.528 -1.468 -1.675 -1.675
(2) f R / f    2.062 2.056 2.069 2.108 2.108
(3) | f F / f R | -0.753 -0.743 -0.709 -0.794 -0.794
(4) D1 / f 3.166 3.179 3.139 2.946 2.946
(5) D2 / f 1.274 1.217 1.395 1.535 1.535
(6) D1 / D2 2.486 2.613 2.25 1.92 1.92
(7) f 3 / f 2 3.008 2.962 2.681 2.55 2.55
(8) | R c | / f    1.561 1.629 1.493 1.639 1.639
(9) TW     -10.032 -10.411 -10 -7.365 -7.59

Example 6 Example 7 Example 8 Example 9 Example 10
(1) f F / f    -1.583 -1.591 -1.623 -1.59 -1.783
(2) f R / f    2.163 2.179 2.08 2.16 2.457
(3) | f F / f R | -0.732 -0.73 -0.78 -0.736 -0.726
(4) D1 / f 3.307 3.385 3.361 3.320 3.96
(5) D2 / f 1.362 1.372 1.356 1.361 1.4
(6) D1 / D2 2.428 2.467 2.478 2.440 2.829
(7) f 3 / f 2 2.612 2.673 2.555 2.601 1.996
(8) | R c | / f    1.649 1.644 1.666 1.649 2.032
(9) TW     -9.433 -9.563 -10.863 -9.529 -7.277

Example 11 Example 12 Example 13 Example 14 Example 15
(1) f F / f    -1.847 -1.853 -1.482 -1.598 -1.742
(2) f R / f    2.395 2.382 1.927 2.159 2.37
(3) | f F / f R | -0.771 -0.778 -0.769 -0.74 -0.735
(4) D1 / f 3.975 3.976 2.866 3.217 3.792
(5) D2 / f 1.408 1.415 1.28 1.409 1.456
(6) D1 / D2 2.822 2.81 2.239 2.284 2.605
(7) f 3 / f 2 1.733 1.705 2.973 2.115 2.125
(8) | R c | / f    1.698 1.693 1.256 1.19 2.061
(9) TW     -8.003 -8.17 -11.235 -9.216 -8.876

Example 1 Example 2 Example 3 Example 4 Example 5
f 1 1 1 1 1
f F -1.553 -1.528 -1.468 -1.675 -1.675
f R 2.062 2.056 2.069 2.108 2.108
D1 3.166 3.179 3.139 2.946 2.946
D2 1.274 1.217 1.395 1.535 1.535
f 2 2.779 2.848 2.916 2.608 2.608
f 3 8.358 8.438 7.818 6.652 6.652
R c -1.561 -1.629 -1.493 -1.639 -1.639

Example 6 Example 7 Example 8 Example 9 Example 10
f 1 1 1 1 1
f F -1.583 -1.591 -1.623 -1.59 -1.783
f R 2.163 2.179 2.08 2.16 2.457
D1 3.307 3.385 3.361 3.320 3.96
D2 1.362 1.372 1.356 1.361 1.4
f 2 2.93 2.954 2.878 2.932 3.373
f 3 7.655 7.896 7.355 7.625 6.734
R c -1.649 -1.644 -1.666 -1.649 -2.032

Example 11 Example 12 Example 13 Example 14 Example 15
f 1 1 1 1 1
f F -1.847 -1.853 -1.482 -1.598 -1.742
f R 2.395 2.382 1.927 2.159 2.37
D1 3.975 3.976 2.866 3.217 3.792
D2 1.408 1.415 1.28 1.409 1.456
f 2 3.371 3.378 2.581 2.946 3.274
f 3 5.841 5.758 7.673 6.229 6.957
R c -1.698 -1.693 -1.256 -1.19 -2.061
　図２２は、本実施形態の斜視対物光学系を用いた内視鏡装置の構成例である。内視鏡装置２０は、斜視用内視鏡２１（以下、「内視鏡２１」という）と、ビデオプロセッサ２２と、モニタ２３と、を備える。内視鏡２１は、挿入部２１ａと信号ケーブル２１ｂとを備える。挿入部２１ａ先端には、斜視対物光学系２４が配置されている。斜視対物光学系２４は、ここでは、前方視観察用の斜視対物光学系である。この斜視対物光学系２４には、実施例１～１５のいずれかの斜視対物光学系が用いられる。 FIG. 22 is a configuration example of an endoscope apparatus using the perspective objective optical system of the present embodiment. The endoscope apparatus 20 includes a perspective endoscope 21 (hereinafter referred to as “endoscope 21”), a video processor 22, and a monitor 23. The endoscope 21 includes an insertion portion 21a and a signal cable 21b. A perspective objective optical system 24 is disposed at the distal end of the insertion portion 21a. Here, the perspective objective optical system 24 is a perspective objective optical system for front-view observation. As this perspective objective optical system 24, any one of the perspective objective optical systems of Examples 1 to 15 is used.
　また、ここでは図示していないが、この斜視対物光学系２４の近傍には、被写体２５を照明するための照明光学系が配置されている。この照明光学系は、光源と、照明光学素子と、光ファイバーバンドルと、を有する。光源としては、例えば、発光ダイオード（ＬＥＤ：Light　Emitting　Diode）やレーザダイオード（ＬＤ：Laser　Diode）の発光素子がある。照明光学素子としては、例えば、レンズ素子がある。レンズ素子は、照明光を拡散又は集光する機能を備えている。光ファイバーバンドルは、照明光を内視鏡２１に伝送する。 Although not shown here, an illumination optical system for illuminating the subject 25 is arranged in the vicinity of the oblique objective optical system 24. The illumination optical system includes a light source, an illumination optical element, and an optical fiber bundle. Examples of the light source include a light emitting diode (LED: Light Emitting Diode) and a laser diode (LD: Laser Diode). An example of the illumination optical element is a lens element. The lens element has a function of diffusing or condensing illumination light. The optical fiber bundle transmits illumination light to the endoscope 21.
　また、内視鏡２１は信号ケーブル２１ｂを介して、ビデオプロセッサ２２に接続されている。斜視対物光学系２４によって結像された被写体２５の像は、撮像素子で撮像される。撮像された被写体２５の像は、ビデオプロセッサ２２に内蔵された電気回路系によって映像信号に変換される。映像信号に基づいて、モニタ２３上に被写体の画像２６が表示される。 Further, the endoscope 21 is connected to the video processor 22 via the signal cable 21b. An image of the subject 25 imaged by the squint objective optical system 24 is captured by an image sensor. The captured image of the subject 25 is converted into a video signal by an electric circuit system built in the video processor 22. A subject image 26 is displayed on the monitor 23 based on the video signal.
　なお、このビデオプロセッサ２２の内部には、ＬＥＤ等の光源を駆動する電気回路系が設けられている。 In the video processor 22, an electric circuit system for driving a light source such as an LED is provided.
　また、ＬＥＤやＬＤなどの発光素子を内視鏡２１内に設けることで、内視鏡２１の外部に光源を設ける必要がなくなる。さらに、これら発光素子を内視鏡２１の先端部に設けることで、照明光を伝送する光ファイバーバンドルを設ける必要がなくなる。 Also, by providing a light emitting element such as an LED or LD in the endoscope 21, it is not necessary to provide a light source outside the endoscope 21. Furthermore, providing these light emitting elements at the distal end portion of the endoscope 21 eliminates the need to provide an optical fiber bundle for transmitting illumination light.
　さらに、光源については、キセノンランプやハロゲンランプ等を用いても良い。また、内視鏡装置２０では、光源を内蔵した光源装置がビデオプロセッサ２２と一体になっている。しかしながら、光源装置はビデオプロセッサ２２と別体に構成されていても良い。この場合、光源装置とビデオプロセッサ２２は、内視鏡２１と各々接続されることになる。 Furthermore, a xenon lamp or a halogen lamp may be used as the light source. In the endoscope apparatus 20, a light source device incorporating a light source is integrated with the video processor 22. However, the light source device may be configured separately from the video processor 22. In this case, the light source device and the video processor 22 are connected to the endoscope 21, respectively.
　以上の説明のように、本発明の斜視対物光学系によれば、組立性や内視鏡先端部への取り付け性を向上しながらも、多画素化と小型化がされた撮像素子に最適な高性能で小型な斜視対物光学系を提供することができる。更に、本発明の斜視対物光学系を用いることにより、高画質の画像が得られると共に、細径化された先端部を有する斜視用内視鏡を提供することができる。 As described above, according to the perspective objective optical system of the present invention, it is most suitable for an image pickup device having a large number of pixels and a small size while improving assemblability and attachment to an endoscope tip. A high-performance and compact perspective objective optical system can be provided. Furthermore, by using the perspective objective optical system of the present invention, a high-quality image can be obtained, and a perspective endoscope having a thinned tip can be provided.
　以上、本発明の種々の実施形態について説明したが、本発明は、これらの実施形態のみに限られるものではなく、その趣旨を逸脱しない範囲で、これら実施形態の構成を適宜組合せて構成した実施形態も本発明の範疇となるものである。 Although various embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and may be implemented by appropriately combining the configurations of these embodiments without departing from the spirit of the present invention. The form is also within the scope of the present invention.
（付記）
　なお、これらの実施例から以下の構成の発明が導かれる。
（付記項１）
　物体側から順に、負レンズからなる前側レンズ群と、光路変換素子と、明るさ絞りと、正の屈折力を有する後側レンズ群と、から構成され、
　後側レンズ群は、正レンズと、正の屈折力を有する接合レンズと、からなり、
　接合レンズは、物体側から順に、正レンズと負レンズとで構成され、
　以下の条件式（１）、（２）、（３）を満足することを特徴とする斜視対物光学系。
　－２．０＜ｆF／ｆ＜－１．３　　　（１）
　１．７＜ｆR／ｆ＜２．７　　　（２）
　０．６３＜｜ｆF／ｆR｜＜０．８８　　　（３）
　ここで、
　ｆFは、前側レンズ群の焦点距離、
　ｆRは、後側レンズ群の焦点距離、
　ｆは、斜視対物光学系全系の焦点距離、
である。 (Appendix)
In addition, the invention of the following structures is guide | induced from these Examples.
(Additional item 1)
In order from the object side, the front lens group including a negative lens, an optical path conversion element, an aperture stop, and a rear lens group having a positive refractive power,
The rear lens group includes a positive lens and a cemented lens having a positive refractive power.
The cemented lens is composed of a positive lens and a negative lens in order from the object side.
A perspective objective optical system satisfying the following conditional expressions (1), (2), and (3):
-2.0 <f F /f<-1.3 (1)
1.7 <f R /f<2.7 (2)
0.63 <| f F / f R | <0.88 (3)
here,
f F is the focal length of the front lens group,
f R is the focal length of the rear lens group,
f is the focal length of the entire oblique objective optical system,
It is.
（付記項２）
　以下の条件式（４）、（５）を満足することを特徴とする付記項１に記載の斜視対物光学系。
　２．４＜Ｄ１／ｆ＜４．４　　　（４）
　１．１＜Ｄ２／ｆ＜１．７　　　（５）
　ここで、
　Ｄ１は、前側レンズ群の負レンズの像側面から明るさ絞りまでの空気換算長、
　Ｄ２は、後側レンズ群の最終レンズの像側面から像面までの空気換算長、
　ｆは、斜視対物光学系全系の焦点距離、
である。 (Appendix 2)
The perspective objective optical system according to Additional Item 1, wherein the following conditional expressions (4) and (5) are satisfied.
2.4 <D1 / f <4.4 (4)
1.1 <D2 / f <1.7 (5)
here,
D1 is the air equivalent length from the image side surface of the negative lens of the front lens group to the aperture stop,
D2 is the air equivalent length from the image side surface to the image surface of the final lens in the rear lens group,
f is the focal length of the entire oblique objective optical system,
It is.
（付記項３）
　以下の条件式（６）を満足することを特徴とする付記項１又は付記項２に記載の斜視対物光学系。
　１．７＜Ｄ１／Ｄ２＜３．１　　　（６）
　ここで、
　Ｄ１は、前側レンズ群の負レンズの像側面から明るさ絞りまでの空気換算長、
　Ｄ２は、後側レンズ群の最終レンズの像側面から像面までの空気換算長、
である。 (Appendix 3)
The perspective objective optical system according to Additional Item 1 or Additional Item 2, wherein the following conditional expression (6) is satisfied.
1.7 <D1 / D2 <3.1 (6)
here,
D1 is the air equivalent length from the image side surface of the negative lens of the front lens group to the aperture stop,
D2 is the air equivalent length from the image side surface to the image surface of the final lens in the rear lens group,
It is.
（付記項４）
　以下の条件式（７）を満足することを特徴とする付記項１から３のいずれか１項に記載の斜視対物光学系。
　１．５＜ｆ3／ｆ2＜３．１　　　（７）
　ここで、
　ｆ2は、後側レンズ群の正レンズの焦点距離、
　ｆ3は、後側レンズ群の接合レンズの焦点距離、
である。 (Appendix 4)
The perspective objective optical system according to any one of additional items 1 to 3, wherein the following conditional expression (7) is satisfied.
1.5 <f 3 / f 2 <3.1 (7)
here,
f 2 is the focal length of the positive lens in the rear lens group,
f 3 is the focal length of the cemented lens in the rear lens group,
It is.
（付記項５）
　以下の条件式（８）を満足することを特徴とする付記項１から４のいずれか１項に記載の斜視対物光学系。
　１．１＜|Ｒc|／ｆ＜２．１　　　（８）
　ここで、
　Ｒcは、後側レンズ群の接合レンズの接合面の曲率半径、
　ｆは、斜視対物光学系全系の焦点距離、
である。 (Appendix 5)
The perspective objective optical system according to any one of additional items 1 to 4, wherein the following conditional expression (8) is satisfied.
1.1 <| R c | / f <2.1 (8)
here,
R c is the radius of curvature of the cemented surface of the cemented lens in the rear lens group,
f is the focal length of the entire oblique objective optical system,
It is.
（付記項６）
　以下の条件式（９）を満足することを特徴とする付記項１から５のいずれか１項に記載の斜視対物光学系。
　－１７°＜ＴＷ＜０°　　　（９）
　ここで、
　ＴＷは、最大像高時の像面への光線入射角度、
である。 (Appendix 6)
The perspective objective optical system according to any one of additional items 1 to 5, wherein the following conditional expression (9) is satisfied.
-17 ° <TW <0 ° (9)
here,
TW is the light incident angle on the image plane at the maximum image height,
It is.
（付記項７）
　付記項１から６のいずれか１項に記載の斜視対物光学系を備えることを特徴とする斜視用内視鏡。 (Appendix 7)
An oblique endoscope comprising the oblique objective optical system according to any one of additional items 1 to 6.
　以上のように、本発明は、組立てや内視鏡先端部への取り付けを高精度且つ容易に行えると共に、高性能で小型な斜視対物光学系に有用である。また、高画質の画像が得られると共に、細径化された先端部を有する斜視用内視鏡に有用である。 As described above, the present invention can be easily assembled and attached to the distal end portion of the endoscope with high accuracy and is useful for a high-performance and compact perspective objective optical system. Moreover, it is useful for a perspective endoscope having a high-quality image and having a thinned tip.
　ＧＦ　前側レンズ群
　ＧＲ　後側レンズ群
　Ｌ１、Ｌ２、Ｌ３、Ｌ４　レンズ
　Ｓ　明るさ絞り
　Ｐ　プリズム
　Ｆ１、Ｆ２　フィルタ
　ＧＬ　ガラスリッド
　ＣＧ　カバーガラス
　Ｉ　像面
　１、５、９　斜視対物光学系
　２、６、１０　前側レンズ群
　３、７、１１　プリズム
　４、８、１２　後側レンズ群
　１３、１４、１６　枠部材
　１３ａ、１３ｂ、１４ａ、１４ｂ、１６ａ　嵌合部
　１５　撮像素子
　１７、１８　斜視対物光学系
　２０　内視鏡装置
　２１　斜視用内視鏡
　２２　ビデオプロセッサ
　２３　モニタ
　２４　斜視対物光学系
　２５　被写体
　２６　被写体の画像 GF Front lens group GR Rear lens group L1, L2, L3, L4 Lens S Brightness stop P Prism F1, F2 Filter GL Glass lid CG Cover glass I Image plane 1, 5, 9 Perspective objective optical system 2, 6, 10 Front lens group 3, 7, 11 Prism 4, 8, 12 Rear lens group 13, 14, 16 Frame member 13a, 13b, 14a, 14b, 16a Fitting portion 15 Imaging element 17, 18 Perspective objective optical system 20 Internal view Mirror device 21 Endoscope for perspective 22 Video processor 23 Monitor 24 Perspective objective optical system 25 Subject 26 Subject image

Claims (2)

  1. 　物体側から順に、負レンズからなる前側レンズ群と、光路変換素子と、明るさ絞りと、正の屈折力を有する後側レンズ群と、から構成され、
    　前記後側レンズ群は、正レンズと、正の屈折力を有する接合レンズと、からなり、
    　前記接合レンズは、物体側から順に、正レンズと負レンズとで構成され、
    　以下の条件式（１）、（２）、（３）を満足することを特徴とする斜視対物光学系。
    　－２．０＜ｆF／ｆ＜－１．３　　　（１）
    　１．７＜ｆR／ｆ＜２．７　　　（２）
    　０．６３＜｜ｆF／ｆR｜＜０．８８　　　（３）
    　ここで、
    　ｆFは、前記前側レンズ群の焦点距離、
    　ｆRは、前記後側レンズ群の焦点距離、
    　ｆは、前記斜視対物光学系全系の焦点距離、
    である。     In order from the object side, the front lens group including a negative lens, an optical path conversion element, an aperture stop, and a rear lens group having a positive refractive power,
    The rear lens group includes a positive lens and a cemented lens having a positive refractive power,
    The cemented lens is composed of a positive lens and a negative lens in order from the object side,
    A perspective objective optical system satisfying the following conditional expressions (1), (2), and (3):
    -2.0 <f F /f<-1.3 (1)
    1.7 <f R /f<2.7 (2)
    0.63 <| f F / f R | <0.88 (3)
    here,
    f F is the focal length of the front lens group,
    f R is the focal length of the rear lens group,
    f is the focal length of the entire oblique objective optical system,
    It is.
  2. 　請求項１に記載の斜視対物光学系を備えることを特徴とする斜視用内視鏡。 An oblique endoscope comprising the oblique objective optical system according to claim 1.
PCT/JP2015/082288 2015-02-20 2015-11-17 Oblique-view objective optical system and oblique-view endoscope equipped with same WO2016132613A1 (en)

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CN201580027281.2A CN106461920B (en) 2015-02-20 2015-11-17 Strabismus objective lens optical system and the endoscope for having strabismus objective lens optical system
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